How can I have a sentient dungeon (or race thereof) in my story?

Question

Lately I have seen many books (e.g.) that work on the premise of a dungeon being a sentient creature. In those books dungeons are large crystals that are capable of creating monsters as well as traps through various methods. They are killed when their crystal is destroyed.

How can I have a similar setting element in my own story? Is there a race similiar to those dungeon crystals or is there a spell that can be used to create a living creature that will control a certain building, doing repairs to it and expanding it whilst protecting it from intruders? Homebrew races are also acceptable.

Answer 1

"Construct" a Dungeon (pun intended)....

After some research spawned by A_Soo's comment/suggestion, I have discovered another option.

The Stronghold Builder's Guidebook is a 3.0 source (but as it was never updated to 3.5 it is still current material for all 3.x games) that covers in extensive detail constructing any sort of stronghold: a lonely wizards tower, a cottage, a minor keep, a huge castle, a dungeon complex... even mobile strongholds are covered: walking, swimming, flying; not to mention traps, wondrous architecture, magic items, portals, multi-dimensional aspects, and more.

Some points of note:

Stronghold Space: An abstract measure of volume within a building. While stronghold spaces don’t have a fixed size, an average stronghold space is equivalent to a 20-foot-by-20-foot room with a 10-foot-high ceiling.

Table 1–4: Stronghold Sizes

Stronghold Type	Size in Stronghold Spaces
Cottage	1
Simple house	4
Grand house	7
Mansion	15
Border tower	4
Keep	12
Castle	20
Huge castle	80
Small dungeon*	30–60
Medium dungeon**	60–120
Large dungeon†	120 and up

*Such as the sample dungeon provided in Chapter 4 of the DUNGEON MASTER’s Guide.
**Such as the dungeon found in The Sunless Citadel.
†Such as the Crater Ridge Mines found in Return to the Temple of Elemental Evil.

Wondrous Architecture: Essentially a stationary magic item. Wondrous architecture often covers an entire stronghold space.

(Note that a Wondrous Architecture could also cover more than one stronghold space... you simply calculate how many spaces you want to cover and then pay the cost of the effect x the number of spaces covered.)

You can tie your stronghold’s mobility to a single object within the stronghold (which may be activated by anyone touching the object and uttering a command word), a location within the stronghold (which may be activated by anyone standing within the location and uttering a command word) or to a single creature within the stronghold (who can activate the movement from anywhere within the stronghold with a command word).

(The keyed item or room or creature mentioned here is what could become the Dungeon Core. There are a number of large crystal orbs mentioned in the SBG, normally used for weather control, but they could certainly be repurposed as a DungeonCore.)

Remember that dungeons are a form of stronghold. Even when you’re not building strongholds for characters, you can use the wondrous architecture presented here to spice up your dungeons.

So, combining all of these with DMG p.269, Table 7–30: Item Intelligence, Wisdom, Charisma, and Capabilities which indicates the cost for making an item... such as a crystal orb or stronghold space... intelligent. In order to make an entire dungeon intelligent, you'd simply need to pay the Base Price Modifier from Table 7-30 times the number of stronghold spaces your dungeon takes up.

The Leadership feat provides minions, the Landlord feat (from the SBG) provides a pool of funds to build (or expand) a dungeon, and once your dungeon is intelligent...

Intelligent items can actually be considered creatures because they have Intelligence, Wisdom, and Charisma scores. Treat them as constructs (see page 307 of the Monster Manual). Intelligent items often have the ability to illuminate their surroundings at will (as magic weapons do); many cannot see otherwise.

... the dungeon is now considered a massive construct in it's own right. Once it is a construct, it could take construct levels in order to gain more hit points and feats and skill points, not to mention potentially other class levels.

The Monster Manual gives the rule we need to allow Intelligent items to gain construct hit dice:

Increased Hit Dice: Intelligent creatures that are not humanoid in shape, and nonintelligent monsters, can advance by increasing their Hit Dice. Creatures with increased Hit Dice are usually superior specimens of their race, bigger and more powerful than their run-of-the-mill fellows.

There is even a type of ooze which can summon creatures... just in case you want to go all literal with your linked example. Maybe it could be your first cohort or minion.

So, go all crazy and build the Goblin Labyrinth from the movie, or have fun starting off with a single room.

Answer 2

I don't know of any monsters that are a perfect match for your description (sentient dungeon with a "core" deep inside the dungeon that kills the monster when destroyed). However, there are a fair few things that kind of fit, or could fit with some refluffing and adaptation. I'll present a few options here for you to either use, or draw ideas from when homebrewing.

Genius Loci

A Genius Loci is probably the closest to what you're looking for. It's a colossal ooze - so colossal, in fact, that it's less an ooze and more a place. It takes the form of the landscape, enslaving or attacking creatures that attempt to pass through it. It could easily be modified to take the form of a cave system or similar, instead of surface terrain.

The downside here is that it's an epic creature, with 70 hit dice and a DC 53 will save to avoid being enslaved, so probably won't work in your game without modifications, unless you happen to be playing in epic levels and didn't mention it.

Colour Out of Space

(Pathfinder, but easily adapted for 3.5.)

A colour out of space is an incorporeal ooze that falls from the sky, hides in dark places, and feeds on all nearby life as part of its reproductive cycle, causing creatures to become aggressive in the process. You could have one of these in the depths of your dungeon, and have it be the reason for the rest of the dangers the party faces.

In this case it wouldn't exactly be the dungeon that's sentient, it'd be something down in the dungeon that's causing the rest of what's down there to attack. But it would result in your "have to find and kill the core to pacify the rest of the place" scenario.

Aboleth

Again, this isn't a sentient dungeon, it's a creature. However, the M.O. of aboleths is to hide at the bottom of their cave systems, and use enslaved creatures and illusions to discourage intruders.

An aboleth could easily seem like it was a sentient dungeon - all the creatures in the dungeon are guided by a single will (the aboleth is mind-controlling all of them), the walls seem to change, conceal traps, and reach out to attack the party (illusions), etc. Only when they get to the bottom of it will the party realize it wasn't the entire dungeon out to get them, it was a creature messing with their minds and the minds of the other denizens.

Dungeon Lord PrC

(from Dungeonscape)

A prestige class focused on absolute control over a specific domain. If you end up using a creature to represent your dungeon, consider giving it levels of this class.

Abilities include being able to see and hear anything that takes place within your dungeon, animating objects in the dungeon, and lots of minions.

Answer 3

Consider your D&D history

Ye olde venerable adventure B2 Keep on the Borderlands inspired the 2nd ed reboot Return to the Keep on the Borderlands which had a unique monster: A Mimic which had grown so large, that it took the form of a mysterious lonely tower which appeared and disappeared. It was alluded to in the Rumors section as "the shy tower", and something to stay away from... which was adventure module speak for "Hey players! There's something over here!!" The module referred to it as a "House Hunter", a huge relative of a mimic so large that it mimics buildings instead of furniture.

A bag of devouring (an interesting cursed item) was also unique in that it was casually described such that the bag was actually the mouth of an extradimensional beastie, without much additional information. Here is the quote from the DMG:

Bag of Devouring: This bag appears to be an ordinary sack. Detection for magical properties makes it seem as if it were a bag of holding. The sack is, however, a lure used by an extradimensional creature—in fact, one of its feeding orifices.

These might also make for interesting variants on the theme.

Answer 4

You really do not need rules for this. Just say that the dungeon is alive, accept the conceits inherent in the dungeon core stories as the background and then be willing to put in the work to constantly update it as you go.

If you want a REASON for sentient dungeons, well there used to be a wizard ruled nation where rather than go to battle with each other they tried to out do each other with complex and challenging dungeons. In time they invented sentient dungeons, some were devoured by their own creations, others simply left, and some still reside within their 'pets' as immortal liches, or as the mind of the dungeon itself.

In my world the dungeons gained enough power to withdraw themselves into a series of pocket dimensions now linked up to form a vast and terrifying network of dungeons linked by portals, wormholes and teleport pads. Collectively known as The Labyrinth or The Dungeon Dimension.