# Problems with minecraft happy druids

We have a highly creative player that plays a druid. This PC tries to make "big digs" from the surface to any underground complex (crypts, strongholds, etc). He uses a combination of conjure animals (giant badgers for digging) and wall of stone (for pillars and beams). With this combination he can safely dig an average of 200 ft./ a day. with two casts of Wall of stone and a bunch of casts of conjure animals.

The first time he did this I congratulated him, it was a great idea and made a great story. But I don't want the party to try to exploit this tactic every single time.

I tried to solve the problem be warning them that they've been caught by tossing a regular encounter with a few guards at them. They keep digging after that, so I threw an oversized encounter at them, forcing them to retreat by means of teleportation magic.

The first problem that this method has is that it takes time. Unfortunately, my party ignores deadlines.

Notes:

This party comes from a long LONG experience with a brutal DM with an alarming record of tpks, none of their PC's ever survived a campaign, this makes them extremely paranoid, they don't take risks unless forced to. Therefore they ignore deadlines, they prefer to let the world burn rather than make a decision that puts them in danger.

This makes things a bit hard for me, I can't put a deadline on them, they're used to stupidly deadly encounters, they tend to fight to the death, and they hate when I tell them to stop using cheesy plans and try to build an epic story.

Keeping all this in mind, I'm looking for ways to prevent them from digging into the BBEG main base.

• Wait... so they won't care if the BBEG achieves his goals while they're tunneling? They wouldn't care if BBEG destroys town/kingdom/world while they're digging a hole? – PipperChip Apr 7 '16 at 17:15
• Hey all, I wanted to remind you all that you should be answering from experience according to Good Subjective, Bad Subjective - the problem and techniques tags don't mean "just give your opinion," please. Good answers will illustrate solutions you've used or seen used to similar problems. – mxyzplk - SE stop being evil Apr 8 '16 at 13:39

# Use scouts

Digging and building mineshafts is very easy to detect for even a casual observer. The BBEG can wait until the druid has wasted a bunch of his spells, then show up and bury the intruders in the grave they just dug. If it's an ambush, the PCs won't be able to teleport away without taking a few hits, and if they have a reputation for being flighty, the BBEG is likely to use poisons, diseases, curses, and other ongoing problems that won't be solved by a quick rest.

# Use consequences for a slow approach

When the BBEG sees the PCs digging, he can predict where they'll end up and trap/reinforce that area of the lair. The PCs break into the lair, and it's flooded with neurotoxin or acid. This goes double if the PCs run away and then try to come back - the area will be swarming with minions, there will be defenses erected, and so forth. The BBEG may send his own spies out to find the PCs' base (or things they care about) and issue a retributive strike.

# Use their reputation against them

Digging big ol' holes in the ground is far from business as usual in the realm of fantasy warfare. Stories of their weird tunneler types will spread, and evil overlords everywhere will defend their bases against this approach. The simplest solution is to bury explosive devices in multiple layers, so that the digging animals are killed and the druid needs to use another spell.

# Use special terrain

Digging in dirt is easy. Digging through mud is easy, but maintaining the shaft afterwards is hard. Digging through granite is all but impossible. Digging through lava gets you dead. Digging into another plane or into a sky fortress makes no sense. If there's an underground river, digging underneath it becomes a challenge - you need to keep all that water out.

# Use subterranean monsters and lairs

All those badgers are coming from somewhere. Some of them may have already done some digging - and instead of landing into the BBEG's lair, the party lands into a giant badger warren, or a formian hive, or the Underdark.

# Use skill checks

Mine shaft structuring is a complicated business; in real life, it's a job people go to college for. Does your druid have structural engineering knowledge? No? Then he put the support in the wrong place and the mine shaft collapsed.

# Use third parties

There are more people in the world than the BBEG and the PCs. What if the PCs are digging in the middle of a sacred elven grove, and the elves come and ask them to stop? What if all their digging attracted another adventuring party, who decided to storm the citadel the old fashioned way and has already cleaned up by the time the PCs break in? What if the PCs are digging in crown lands, and a magistrate comes and demands to see their zoning permit?

• +1. Also, re third parties: what if this is a really cool tunnel that is just lying there defended for use by. . .? :) – Lexible Apr 8 '16 at 2:04
• Re Third parties: you could also let them do their thing slowly and let another group of heroes fight their way through the entrance and save the day (or the world). With everybody celebrating the new heroes, these adventurers should be well motivated to try something faster next next time. – Peter S. Apr 8 '16 at 10:23
• +1 for the subterranean lairs. Sometimes players are hell-bent on going off the reservation, and it's better to throw something interesting in their path than to try to railroad them through the exact path you want. – Blue Footed Booby Apr 8 '16 at 13:22
• As far as third parties go, Smaug was wandering around one day, and found a nice hole to live in. So did Shelob. Just saying. :) – Graham Apr 8 '16 at 16:21

Talk to the Players

They are used to being the target of a DM out to kill them. You're a DM trying to let them be the hero. There is still a risk of dying, but you aren't trying to kill them like their former DM was. Tell them that they can, and are encouraged, to try new things and take risks. Specificially talk about their spell and say "It was cool, but I'll be actively discouraging you from using it that way again."

Obsticles that Make it the Dangerous Option

Suggestions that come to mind:

• Make the BBEG's base surrounded by water or very high tower.
• Have a large perimeter around it crawling with gaurds.
• Have a lava flow close the the surface that he exploits for smithing his minion's arms (ala LOTR)
• Let the BBEG know about it and have him devise a trap tailor made to that kind of attempt.

Play the Conjure Animals Spell RAW

Conjure Animals, as written, lets the players pick the level/number, but the DM picks what actually shows up. They can try to get something that digs, but you could make birds appear instead. This change would be different from what you've been playing, then you could run into people problems ("Aw, Com'on! You let us before!").

• "I'm sorry I feel I have let you down. After re-reading the rules of the Conjure Animals as written, it simply doesn't let the caster choose the animal that appears, and we've all been doing it wrong. So here's what I'll do, I'll make a random chart of animals and we'll roll for them...." "oooh, you got an ostrich, now what does he do?" – CGCampbell Apr 8 '16 at 15:58

## What's the Real Problem?

It's not that hard to make digging hurt; you can set up wherever they dig into to be more or less equivalent to the gatehouse they would storm if they went in the normal way, for instance.

However, what you seem to really be having issues with here are players that want to focus on interesting exploits, rather than traditional narratives.

Now, this could have its own issues associated with it: players could want a different genre, or feel that this is a way to get agency that they aren't getting through more traditional applications of their character, but I'm going to go ahead and assume that those aren't the issues.

### Make Time Matter

You mentioned that your players blow off timelines. Don't let them do this. Now, obviously you can't force them to do stuff; teleporting them into a boss fight with the dude what needs killing is only fair or interesting once or twice tops, and you need a fair deal of setup to get that to work. Likewise, having the objective they need to complete come to them is going to be problematic as well.

With the tunneling thing, there are tons of things you could do to remove the tunneling, but this could lead to other exploits. What if the players are content to summon giant eagles and bombard the fortress with boulders?

If they don't meet the deadline, the quest fails. They don't get a reward, because the reason they were sent to stop the guy has already become outdated. Either the BBEG's plans succeeded, the quest-giver died at the hands of an assassin, or they simply get scolded for taking too long.

### Communicate Expectations

One thing you mentioned is that your players are used to a very brutal DM who just killed them a lot. You need to make clear that you are not that way. You can suggest things like Schrodinger's Dice, where players roll for their characters' deaths in secret and are never challenged on the dice: if they go down in a fight they'll be alive unless something finishes them off (if they desperately want it enough to cheat), and you control the bad guys so they won't be finished off.

Someone in comments mentioned the Same Page Tool; there are a lot of other ways to do this, but basically have a heart-to-heart with your players and mention your concerns with the group's planning. It may turn out that they like shenanigans like this, and then you have to decide whether or not to allow it or to encourage them to move away from it.

### Emergent vs. Scripted Events

One thing to consider as well is the nature of the game: role-playing games offer an incredible amount of flexibility in actions and storytelling, and emergent play (in which outcomes are based on freely selected actions) often is a result, as opposed to scripted play (in which outcomes are based on a limited selection of actions).

Talk to your players, and ask them if they'd be fine playing more genre-traditional strategies. If not, recognize their emergent play and make it part of the setting. Enemies learn from their mistakes: if the characters let their secrets slip, or let any of the BBEG's minions survive to tell the tale, every villain they encounter has planned for their schemes. Let them know this: each strategy only works once.

Part of this is pushing the deadline. If the villain knows they'll take fourteen days to tunnel into his fortress, the appropriate response might mean setting off the doomsday device on day seven. Be fair with this, of course, and make sure that the players know that there is urgency. Heroes can say no to the mission parameters: they're not typically soldiers (though if they were you could throw insubordination at them) of the crown or anything like that, but they can't say no to harsh realities of their enemies' victories.

They say there are things in the earth that should remain buried.

Do you remember the fate of the Dwarves of Moria?

Something could be unveiled; something wrong that changes the dynamic of the setting/party and puts them out of their comfort zone. Not as players, but as characters in the game.

In my head I have some weird quest hook - the druid's animals unveiled a potent ancient plague and became infected. What will the druid do and feel, knowing that he is the sole cause of their suffering? What will happen to the world if an old plague takes hold of it now, when modern creatures are susceptible?

The implication would not be a TPK but something really unsettling and world-changing.

Another way to handle it would be to let players have their way. They might get bored and change their tactics to make the game more enjoyable.

How about letting your BBEG react to the players' plans? Perhaps he has the means to counter their attack vector? I don't know your BBEG's capabilities so I can't give more advice here.

But I have a horrible picture in my head: the druid digs a pit with help of his squirrels, but the BBEG sends a 'squirrel-vampire' (an undead creature that can replicate by killing/turning other squirrels, or otherwise sabotage the workforce {mind-controlling fungus, anyone?}) and it cripples the excavation efforts, while also creating a threat that grows exponentially. What could the players do to prevent a disaster that can wipe out their digging force?

You could use fantasy terrain that is actively dangerous for digging. For example, earth mixed with broken glass, a literal Glass Field, or a swampy area where any tunnels flood quickly.

As a side-note, has the druid thought about his impact on the ecosystem? His mass diggings are sure to impact the normal lives of forest creatures. What the hell, hero?!

• I think the last one is one of the most important one considerations. Can a Druid be a civil engineer? Seems like there could be a bit of conflict there. – KevinO Apr 7 '16 at 19:42

## Talk to your group to develop a mutual understanding and set campaign expectations.

You seem to understand a lot of causes for the issue at hand. Tell your group that you understand they're risk-averse but that you're not interested in killing them. Except in extreme circumstances or their total disregard of explicit risk, a TPK is a failure on your part; let them know that you feel this way. Your bad guys can have motivation for capture over killing.

Let them know that you truly appreciate the first time this plan was used. It was resourceful, creative and interesting. However, let them know that you don't want to design a campaign specifically to be bypassed using the same technique, and that such techniques are limited use.

Regarding the deadlines issue, this will be hard behaviour to change immediately, even if they start taking more risks.

Deadlines can be a really interesting way to force players to prioritise and make tough decisions. You could try running sessions that highlight this; for example having a time counter (a d20) tick up every round and keep actions within rounds outside of combat. If somebody gets their leg stuck, the party has to decide whether to spend a tick helping them out or let them arrive late to the critical moment.

Alternatively, you could incentivise sticking to deadlines by having them affect the players. Oh, now it's not just that the princess was captured, but the party is somehow implicated and will be held responsible if they can't fix it. Oh, now a party member has a curse that's gradually worsening.

Or you could just have the rewards become unreachable over time. After a deadline, the bad guys pack up and move on, or they're gradually consuming/destroying a scaling reward.

• IMHO this is the only really correct answer. The problem here has nothing to do with interpretation of spell descriptions or the perils of civil engineering - it's a problem of mismatched group expectations. – MrTheWalrus Apr 13 '16 at 15:05

I have faced similar situations in the past - specifically that I had a group of over-the-top engineers who actually knew a lot about the various topics/subjects that came up. This typically lead to a "this is possible, and within the rules" conversations quite often.

However don't be tricked into following their mindset. You are the DM, by the very nature of the game you should be controlling the flow of events/story. Thats not to say level with the players and be compromising, an ingenuous solution to a tough problem should be part of the experience. Here is some ideas that should help you get through this and still give a great story experience.

1. Just because it is "possible", does not mean it is feasible or safe. I hate to say it - but unless your druid is en expert miner with a background of experience and knowledge his tunnel is probably going to collapse, or at least have a variety of problems.
2. Underground monsters. There is a lot of them, if you feel the party is going to make the entire encounter useless just start throwing monsters at them until they deviate back onto the correct path. Typically I use a factor of 1.5x depending on the distance they are from the main plot to keep them in line (e.g. The first time they step out of line the encounter is 1.5x harder then it was supposed to be, if they continue down that path continue adding to the difficulty and trying to encourage them to backtrack to the proper path).
3. Natural disasters (earthquake, flood, etc). A little heavy handed but entirely possible.
4. Have very hard deadlines known to the players. Things like, "the princess will be killed if you take more than 2 days to rescue her, and the bandits leave with their loot in hand. It is sad for your story, but the players will learn that every quest from that point on should be followed strictly rather then taking their time.
5. Lastly - Just do not allow it. When they pitch the idea simply tell them, "it will not work". They may ask for a reason but you simply have to say something along the lines of "Try it and find out, but it will be a waste of time". This can also be done through in-game RP (such as saying the fortress is magically protected from access other then the front doors).
• Good point. Profession: Miner checks should be required for any substantial shafts. – Loren Pechtel Apr 9 '16 at 5:40

Problem: Your players expect you to both try to kill them with numbers and be an unimaginative GM who does not react to their actions in any way (aka a bad GM).

Solution: Have the bad guys make mistakes.

If you give the players information on what is going on - overhead conversations, diagrams of observed patrol routes, enemies living in mountain chalets with big windows and ineffective walls, that information can reveal vulnerabilities in security design (intentional ones on your part) that will be taken as opportunities by the group. They may ignore a few - thinking them 'traps' designed to 'kill them and it's their fault' so you can gloat about it or whatever bad GM 'orb of annihilation door handle' behaviour they've come to expect - but eventually they'll take one, and they'll feel smart and like badasses and get addicted to doing that, and the 'exploit' style behaviour of treating the game like a CRPG scenario they have to 'break' will quickly disappear in a tide of taking the world as real.

Once someone has their 'trust' in the GM shattered, you need to rebuild that trust by tricking them into trusting by accident and then rewarding that trust with a fair and realistic outcome.

## Play God

According to some of the flavor text in the PHB for druids (pg 64), druids get their power either from a deity or nature itself. Druids strive for balance in nature. Depending on how in line with the DnD lore your players' character is, you may be able to justify a few loss of powers.

What your player is doing is moving literal tons of earth around. This can be argued to upset the delicate ecosystem in which they are tunneling. This is a big no-no for druids generally. Use this as justification to take away your druid's abilities temporarily.

Other answers have suggested numerous defensive mechanisms to protect against tunneling, but I am suggesting you eliminate it altogether. Though, I would advise you only restrict your players if they keep doing the tunneling.

My experience with this type of thing: it creates some tension in the group and also allows for a lot of roleplaying chances. Your druid attempts to conjure animals and nothing happens. Why? Well now they have another quest on their hand, which creates more opportunities for storytelling. Of course, now they must redeem themselves in the eyes of their deity. More fun times!

One final, very important note:

You really need to let them know what kind of campaign you're running and what kind of deadlines they're facing. You could even let them know via some divine intervention, which could be combined with the deity explaining why his powers are missing. How can they know the tunneling is too slow unless you tell them?

• Up-voted, but I must leave this comment. Let's assume GM will use god's intervention to stop player's exploits. From GM's point of view it follows the inner logic of the game world, and is reasonable. And - hey - I really think that in normal circumstances it would be a valid (and depending on setting - even awesome) reaction of game world to player's action. And that reaction of game world is the point of many of my favorite 'game-modes' and 'scenarios' for role-playing games. But. Circumstances here are not 'normal'. If I judge correctly, players from this question are used to be on defense. – Jaiden Snow Apr 8 '16 at 17:31
• Druid's tactic in their view could be a solid defense - they can view it as their achievement to stabilize situation in the game world. If gods will come and strip their creation away, it will look not unlike GMPC (Game Master's PC). It can even be perceived as stripping off their agency - wherever they do - doesn't matter. And if they perceive it that way this will kill their trust and purpose for game. So, using god/nature - could express wrong idea. – Jaiden Snow Apr 8 '16 at 17:31
• @JaidenSnow sure, I agree with that. I made this answer because it was an option I didn't see mentioned. Truth be told, I think taking away powers is not as good as subverting the digging with some of the processes detailed in other answers. But, it's still an option if worse comes to worst, and one that can lead to other quests (which probably isnt what you want if you're on a deadline) – Premier Bromanov Apr 9 '16 at 16:04

It seems to me that most dungeons, especially ones inhabited by a BBEG (big bad evil guy?), tend to be inhabited by a large number of foes, and than going through a dungeon's halls quickly and quietly usually gives an attacking adventuring party an advantage, because they can usually engage most of the enemy forces piecemeal, a few at a time.

Starting a strip mining project on the surface has the advantage of unexpected approach, and unexpected direction/location of entry, but it has the disadvantages of slowness and loud/large announcement of the party's presence, the use of a lot of magic, and the placement of the party in an exposed location, instead of a confined space.

In other words, I would tend to expect a BBEG to notice a mining operation, and use the opportunity to organize a coordinated attack with all the forces he can muster. Also (especially if G stands for genius rather than guy), I would tend to expect a BBEG to use any such obvious warning of an assault on his lair, to collect any valuables and magic items at the lair and move them to some other safe place, and/or use the magic items in the counter-attack, as well as to arrange his own escape from the lair, making the whole attack by the players on the lair somewhat pointless. Sounds like an invitation to TPK rather than a clever way to avoid it. That just seems like probable natural consequences rather than GM meanness, to me.

Honestly, I don't think badgers of any size could really accomplish this. They would really only be suited to surface digging, and would soon begin to tire and become injured. I can't imagine a druid subjecting giant badgers to dig until they bleed, and they would be ineffective once they reached any reasonable depth. Most certainly, even the strongest giant badgers aren't going to be digging through bedrock, which may be as shallow as 50' or less, and likely not through even the compacted earth at the subsoil. Hat's off for ingenuity, but I think the physics is probably the largest constraint.

Remember that as the DM you can simply tell your players that they can't do something. A variety of rationales exist for why they couldn't build a tunnel into a dungeon.

• The ground is unsuitable for tunneling (Rock, Sand, Mud, etc.).
• There are wards on the dungeon that prevent tunneling in. These wards could predate the current inhabitants and thus not require casting by the current inhabitants.
• Ask them to make a wisdom check and tell them they would probably be heard by the inhabitants if they tried tunneling in.

Remember rule 0 and if your players are unable to accept that you are the ultimate authority at the table you might want to have a discussion with them about that.

That being said, try not to overly discourage creativity. It's fine to tell your players no but try not to do it too often.

Every 10 feet of digging, perform a secret D20 roll. Add +1 to the result for every 10 feet of total depth. Only announce when something happens.

1-12  nothing happens
13-15 change in terrain (change at random to solid rock, underground lake, mud, gravel, lava, etc)
17-19 minor accident (rock fall, flood, minor collapse etc) players must make a save or take some damage
20    animal encounter - players had dug into the burrow of a (now furious) underground animal
21    booby trap - players trigger a mine or dig through the roof of a spike pit
22    total cave in - players must make some sort of save or be crushed to death


Details of the list don't really matter. As soon as you start rolling they will realise something is going on. As soon as you announce your first result they will figure it out and be very wary of going any further.

I'd be wary of just hitting them with something really nasty straight off. You don't want to be like their previous brutal DM and tpk them just for trying something out. Best to put the frighteners on and persuade them off their current course of action.

• I got the impression that the summoned animals were doing all of the digging, so cave-ins were just going to cost another casting of animal summoning. Time and progress lost, but not much more than that. (And only doing the rolls while the PCs are inside is going to signal pretty clearly that the GM is out to get them.) – PotatoEngineer Apr 8 '16 at 2:15

When the party wants to do something that is going to take a long time, and you don't want to have to sit there while they try it, you can just use a timeskip and jump over it.

Player: "We're going to dig. So, I start by casting-"

DM (interrupts): "Right! You spend the rest of the day digging. It looks like it will probably take another week to get through. You want to keep going?"

Player: "Yes, we-"

DM: "Ok, you dig through the week. Eventually you make it through. You are now standing at the opening where your tunnel joins the underground lair"

And then keep playing from there, just as if the players had walked in the front door. Or, if it is missing the deadline itself that is the problem, you can use one of the other suggestions here - like maybe you say

"At the end of the week you break through into the underground fortress, just in time to see a party of adventurers walk by, celebrating their victory over [badguy]. Gee, if only you had gotten there sooner..."

That way you can jump over the players messing around, and get straight to the next adventure. If the players keep doing this, by the end of the play session, they may have tunnelled into a dozen different lairs, and been too late every single time. I think by that point, they might just take the hint!

• Or “At the end of the week you break through. The tunnels are all empty and there's no-one home. There are signs of a leisurely evacuation that took, oh, a bit under a week.” – SevenSidedDie Apr 8 '16 at 18:04
• Take care with this approach, lest the message the players learn is "we're not allowed to do anything cool and creative". If I came up with an awesome way to use my spells and abilities to do large-scale excavation and the GM just said "OK, you're digging" without even letting me tell him the plan that I love so much, then I'd feel like he doesn't want to let me do anything interesting. And I'd likely leave the game if it happened more than once. – Dave Sherohman Apr 10 '16 at 8:45

Why not just put your encounters in locations that aren't underground?

Castles? Fortresses? Big towers? Mountains that already have extensive dug-out tunnels beneath the actual location of interest?

It's clear to you, and it should be clear to the Big Bad at this point, that underground is not a safe haven - so just don't give them that option.

My answer is similar to others, but should be different enough to merit a separate entry.

1. Top soil only goes down so far. Eventually you hit rock, and almost any underground fortress is going to be set in rock.

Cave systems are left when water carves passages through rock and stone formations. The material left is hard enough to hold its shape around this void and is not going to be conducive to easy digging.

Mine networks, especially the larger ones, are also usually fairly deep, and also mostly contained within rock formations (that's where the ore is).

2. In locations where that much digging by badgers is possible, it would be a prime territory for ankhegs and bulettes. That much digging will draw a lot of unwanted attention, even if the target of the tunneling remains unaware.

3. Sappers, when used in warfare to bypass or bring down walls, are only possible when the target is unaware, or when in a siege situation and the target is unable to attack, except with their own counter-sapper teams.

As has been said, mining is fairly easy to detect. Can you say "ambush"?

Or, assuming enemies that don't have a problem operating on the surface, counterattack while the party is going down the shaft. A rock rolled in after them could be very nasty indeed. (I would say the BBEG can't quickly find a really big round one so the rock that comes down doesn't TPK them.)

Talk to them.

Don't just make it hard for them to do what they want to do and cripple their plans. Talk to them as a fellow player and person.

"Hey guys, I'm not that previous DM. I'm not out to get you and kill you all and make a throne of your puny player bones. I'm also a player in this game we call D&D. And, really, I'm getting a bit bored with this digging thing. Can we please move on, chums?"

Your players found a really creative solution with a combination of skills and you loved it at first. I'd be cautious about trying to discourage it. That could likely pit the players against the DM and you seem adamant for collaborative versus combative storytelling. Let me offer an alternative.

"Word of the PC exploits has reached far and wide. The heroes from town X, now known as the Badgers, are in great demand to fight the evils of the underground. Finally impossible lairs may be breached!"

Then I would introduce a multitude of situations where this skill is in demand. The King's royal army needs help besieging a castle. The farmers from a town over are loosing cattle to molemen and have an approximate idea where the thieves layer is. Dwarf miners were caught in a collapse and desperately need help.

Let them play with the new toy for awhile. Eventually start introducing adventures that don't involve shaft building. When they are bored of tunneling they will start selecting those. However, I think the name "Badgers" should stick with them.

Terrasque...nuff said. Alternatively some type of Wurm or other colosal burrowing monster is disturbed by the multiple disruptions within its territory during hibernation season. Introduce it with spooky tremors or sudden air pressure shifts in the excavated tunnels so as not to unfairly TPK the party without warning. This monster was not disturbed by the BBEG's dungeon because it's a preexisting structure.

Caveat: Druid floods the tunnels, defeats the deus ex monstrina, the party levels, and your carefully balanced climax dungeon is ruined.

• Do you mean monstrum ex machina? – SevenSidedDie Apr 12 '16 at 20:25

don't know whether that's usual for D&D but even if it's not you could perhaps still apply it because such a digging tactics isn't usual either, you could try a combination of the following:

• a material the moles cannot dig through, surrounding the BBEG base
• a huge sky styled realm where moles and other Earth-typed creatures cannot be summoned and where the only item able to break that material can be found (perhaps the theme would be something like a starlighted frosty summit, in a parallel dimension with an everlasting night, that always comes out fine in video RPGs so why not in D&D?)

by doing that, you would have both solved the problem of the party getting to the BBEG base too easily and prepared an awesome setting for the story

an alternative coming close to this, but still quite similar, would be the following: many RPG videogames and RPG board games (can't think off examples for the latter, all I know is AtmosFear hasn't) have their final in some sort of floating castle of doom, so you could consider apply this idea to your D&D campaign, perhaps even let your players dig down until they hit the walls of the base, which turn out absolutely undiggable, and once they try the earth starts trembling and the castle next to them starts ripping open the ground and emerging into the sky

I must also add the "Talk to the players and regain their trust" item, which is both important for the game and constructive regarding future campaigns, so I subscribe to that point too, try explaining them that you want them to experience what immersion is