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I want to create a demiplane with the spell Demiplane and protect it with a permanent Forbiddance ritual. This would prevent others from gaining access to it via Gate or Plane Shift. But would this also prevent me from using Demiplane in the future to gain access to it? Consider the first sentence of Forbiddance:

You create a ward against magical travel that protects up to 40,000 square feet of floor space to a height of 30 feet above the floor.

It goes on to call out different methods of planar travel, but is not limited to those. By my reading, the door created by Demiplane would cease to work because of the first 2 sentences of the spell:

You create a shadowy door on a flat solid surface that you can see within range. The door is large enough to allow Medium creatures to pass through unhindered. When opened, the door leads to a demiplane that appears to be an empty room 30 feet in each dimension, made of wood or stone.

This shadowy door is objectively magical travel, and thus wouldn't be permitted, right? I have heard some make mention of the disclaimer about a password towards the end of the text of Forbiddance, but that seems to apply only to damage caused by it. This is really just a thought experiment but I wanted to see what you all think.

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4 Answers 4

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Just let forbiddance stop directly before the door

Forbiddance says:

You create a ward against magical travel that protects up to 40,000 square feet of floor space

There is no requirement that this area needs to be in full 5 x 5 foot squares. Just have it stop a few millimeters short of the wall in the area where the door is.

That way, you can enter through the door, without it being affected by Forbiddance, and moving further into the demiplane will be normal movement within it.

Others that try to plane shift into your demiplane, or to open a gate in your demiplane will still have no unprotected space to do so. (Maybe they could squeeze a gate portal in if they knew exactly where the unprotected strip is, but that is very unlikely.)

It is hard enough to find out about a demiplane in the first place. I would certainly also cover it in Mordenkainen's Private Sanctum to block anyone scrying on you getting in or out there, or to spy on you while you are there.

I also think @SeriousBri makes some really good points about how a DM should think about this, apart from any rules mechanics.

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  • \$\begingroup\$ Thank you, this was exactly what I was considering if someone needed to give themselves an explanation for why it might work. \$\endgroup\$
    – SeriousBri
    Commented May 11 at 9:59
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    \$\begingroup\$ +1, and I agree that opening a door to a plane, is different than forbiddance across an area of the plane, even if the area in question is the size of the plane. However, the millimeters trick seems cheesy to me. As a DM, I might allow demiplane to connect to the plane, but it wouldn't be because of a few millimeters of space. And since we don't know how much space a gate takes up, if the millimeters is the only reason to allow demiplane, I see no reason it would disallow gate. \$\endgroup\$
    – Jack
    Commented May 11 at 17:07
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You need a DM

Building things with high-level spells, and how planar travel works, is as much a question of world-building as rules-reading.

Part of the challenge is that the published spells are not a toolkit for creating great magical constructs, but instead an adventuring toolkit, and furthermore one that targets a hugely diverse audience.

We can speculate, we can conduct a thought experiment, but there is no real ruling without a DM.

Will forbiddance stop access via gate or plane shift

It seems likely. Forbiddance says:

creatures can't use portals such as those created by the gate spell

and

. . . prevents creatures from accessing the area by . . . plane shift

That seems pretty straight-forward.

Will it prevent demiplane

That is a little less clear.

Forbiddance does not specifically mention demiplane as one of the spells it prohibits

First of all, forbiddance does not specifically mention demiplane, although it mentions other planar spells. In particular, it says it forbids portals "such as those created by the gate spell", and without an internal logic to planar gates we don't know whether the door created by demiplane creates a portal "such as the gate spell", or something else.

Does "connecting to a demiplane" connect to the plane, or the area within it

Second of all, demiplane connects "to a demiplane you created with a previous casting". Connecting to a demiplane as a whole seems different than opening a portal within the area inside the plane. So is connecting "to a demiplane" different or the same as connecting to the floor space that makes up that plane? As Nobody the Hobgoblin said in their answer, it seems reasonable that its different.

There's not a perfect RAW answer. One DM might say sure, another might say no.

How to approach this

The player and the DM need to work together to realize the player's concept within the DM's concept of the game, while at the same time the DM keeps in mind keeping the game challenging and fun for everyone.

An example

We concluded a high-magic campaign last year that ran in two arcs, from 1st to 13th level, and then from 13th to 20th.

Working with the DM on mundane world-building

At the end of the first arc the party had an instant fortress that they used to set up the core of a base on a hill. We invited an NPC cleric to set up a temple on a nearby hill, and another NPC to set up an observatory on another nearby hill. At the base of the three hills there was a smallish river that flowed to the nearby coast, and a village and eventually a town sprang up there.

Determining that the instant fortress was not big enough, we built an outer keep. The DM never asked us for detailed plans. We discussed what we wanted in general, and the DM told us what was attainable with the wealth and resources we had available. We had a good bit of money, the problem was skilled labor, and time. We ended up having to import an overseer-type NPC (the DM called them a majordomo) who oversaw construction.

We, the players, didn't need to work out every detail of how it worked, and neither did the DM. We worked with the DM to determine enough detail for the story to continue.

That is a mundane example of the DM and players working cooperatively.

Working with the DM on demiplane

Similarly, once we got to 15th level my wizard starting using demiplane. We determined that gate won't connect to a demiplane (created by the spell), and that plane shift might, but that the tuning fork was unique to each demiplane and essentially unknowable.

However, of chief concern to me was the sentence of the spell:

Additionally, if you know the nature and contents of a demiplane created by a casting of this spell by another creature, you can have the shadowy door connect to its demiplane instead.

That seems to invalidate the sanctity of a demiplane, because if "nature and contents" is interpreted broadly enough then connecting to "the plane containing the wizard Xenon's clone" might be possible, and if its narrow enough, it becomes a unique key and loses meaning, and why even include it in the spell.

The DM said, "Okay, tell me how you think it works that gets you what you want without breaking the game."

We went back and forth for a while and eventually determined that the way it works in this world is that the "nature and contents" is so specific that it does in fact represent a unique key, which is represented by the caster of demiplane by a unique sequence of some sort, perhaps a sigil, or words, or musical notes, or some other pattern. Determining the sequence is impossible, short of divine meddling or perhaps wish.

The DM left the door open slightly. My wizard had access to significant research facilities, and actually had researchers working for them. The DM said your research occasionally turns up hints that breaking into demiplane is perhaps possible, but the lead always turns up nothing. But you can't be completely sure that there isn't a way, you've just never found it.

However, I did get demiplanes that were safe enough for our party to use as vaults and safehouses, and for my clone, which was enough to move the game forward, and keep things fun for everyone.

Going further

My wizard always wanted to trade research time for greater arcane discoveries, but time was limited. For instance, I wanted to connect or otherwise expand a particular demiplane. The DM was amenable to the theory and the discussion, but we never actually executed, because my wizard never had the time.

We were too busy saving the world.

At the end of the campaign, after the final battle at 20th level, we retired the characters, and in fact the campaign, and even the setting. The DM gave us the opportunity to provide any afterward we might want, for our party and individual characters, providing an overview of what became of them at the end of the story. My wizard had several things on their list, like irradicating the hidden city of mind flayers that we found, and freeing those they enslaved, but after that my wizard spent much time in research, disappearing from public view for extended periods of time, and came up with all sorts of demiplane tricks. For instance, in their castle there was a semi-permanent door to a demiplane, which itself was expanded and furnished, and then also connected in turn to other demiplanes.

That seems like how some those things in the published materials that can't be done with the adventuring toolkit got there -- some wizard spent inordinate amounts of time to do it, and no, you the current player can't do it, because how they did it isn't known -- exactly the tools they used to do it aren't in the adventuring toolbox. You could figure it out, might take years, but you don't have time right now, because you're busy saving the world.

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TLDR: Your DM needs to decide whether the demiplane is on the same plane you cast it from

How spell descriptions work

In 5e all of the spell text is rules.

That being said, however, it is clear that in practice many spell effects and class abilities are written with two distinct sections in different styles. I think it is useful to consider the two sections as operating from two perspectives, both within the rules but from different parts of the rules. The first describes the feature from an in-character or narrative perspective, while the second relates what the game mechanical effects of the ability are, in the meta-narrative sense1.

Applying this analysis to the Forbiddance spell, we can see that the first sentence describes what the caster knows:

You create a ward against magical travel that protects up to 40,000 square feet of floor space to a height of 30 feet above the floor.

However, "magical travel" is itself very vague. What does it include? Would forbiddance bar me from entering if I was being borne by boots of flying? By a potion of gaseous form? The second and third sentences, however, specify the mechanics of the spell, and what is needed to adjudicate it (emphases mine):

For the duration, creatures can't teleport into the area or use portals, such as those created by the gate spell, to enter the area. The spell proofs the area against planar travel, and therefore prevents creatures from accessing the area by way of the Astral Plane, Ethereal Plane, Feywild, Shadowfell, or the plane shift spell.

The first part of the spell provides a general description of intent, while the second part describe the specifics of how to apply rules to that intent. The second and third sentences explain that within the context of forbiddance, "magical travel" does not mean boots of flying, but it does mean teleport effects and planar travel among other things.

With this in mind, we are now prepared to examine the demiplane spell.

What are demiplanes?

Demiplanes themselves, including but not limited to the ones created by the eponymous spell, are defined as "small extradimensional spaces with their own unique rules" (PHB 302).

The DMG (p. 68) goes into more detail:

Demiplanes are extradimensional spaces that come into being by a variety of means and boast their own physical laws. Some are created by spells. Others exist naturally, as folds of reality pinched off from the rest of the multiverse. Theoretically, a plane shift spell can carry travelers to a demiplane, but the proper frequency required for the tuning fork would be extremely hard to acquire. The gate spell is more reliable, assuming the caster knows of the demiplane.

A demiplane can be as small as a single chamber or large enough to contain an entire realm. For example, a Mordenkainen's magnificent mansion spell creates a demiplane consisting of a foyer with multiple adjoining rooms, while the land of Barovia (in the Ravenloft setting) exists entirely within a demiplane under the sway of its vampire lord, Strahd von Zarovich. When a demiplane is connected to the Material Plane or some other plane, entering it can be as simple as stepping through a portal or passing through a wall of mist.

Some means are given for entering a demiplane that would specifically be barred by forbiddance: plane shift, gate, stepping through a portal. But what about just walking in, as per the spell description? Whether or not that is prohibited magical travel depends on what kind of demiplane the spell creates.

What kind of demiplane is demiplane?

Some demiplanes are not on the Material Plane, such as the Domains of Dread. Where is the demiplane created by the spell? Personally, I find it hard to believe that an 8th level spell can create a permanent, new plane that never existed before. As a DM, I would rule that, at least while the door is present, the demiplane created by the spell operates like a magnificent mansion: it is still on the Material Plane, just in an extradimensional outfold of reality that is pinched off so that the only way to physically access it is through the door. As such, it could be walked into, with the door representing no more than a same-planar but dimensionally-strange access point. Much like sticking your arm into an open bag of holding, where your arm is not transported to another plane, neither would you walking through the shadowy door into a same-plane demiplane magically transport you.

However, your DM might rule that the demiplane created by the spell is actually "someplace else". If it is not on the Material Plane (or whichever plane you are on at the plane of casting), then the doorway is perforce a magical portal, because it must be moving you from one plane to another. This is precisely the kind of "magical travel" that forbiddance bars.

Note also that each time you cast the demiplane spell, you have the option of making a new demiplane or accessing an old one. If your DM rules that your spell merely creates an extradimensional space within the plane you are on, then forbiddance would not stop you from entering it so long as the first duration held. But even with this favorable ruling, if you were later on a different plane and wanted to access a demiplane you had previously made somewhere else, the same forbiddance spell would now bar your entry.

For example; say I cast demiplane on the Material Plane, enter, cast forbiddance, and leave. For the next hour I can freely walk in and out the open door. At the end of an hour the door disappears. If I then use plane shift to go to Avernus, I can cast demiplane again to access my original space, which is still on the Material Plane albeit with no door to the larger plane of which it is a part. However, my own forbiddance spell (duration one day) would now keep me from passing through the door, because the door itself was not acting as a "magical travel" portal from the Hells to the Material Plane.

Conclusion

With a sympathetic DM ruling, you (and and anyone else) who uses the door should be able to walk into your demiplane through the door, unaffected by the non-damaging part of forbiddance. It is only arriving by other means, from somewhere else, that the spell would prohibit. However, if your DM rules that the demiplane is its own plane of existence, then forbidance would bar entry by any means, since no matter where you are arriving from, it is somewhere else and thus the door provided magical transport.


1 As one example, this question asks whether Absorb Elements can be used to damage opponents on the same turn it is cast if an attack is made that same turn, or whether it has to be the next turn, when the spell says (emphases mine):

The spell captures some of the incoming energy, lessening its effect on you and storing it for your next melee attack. [...] Also, the first time you hit with a melee attack on your next turn, the target takes an extra 1d6 damage of the triggering type, and the spell ends.

Here, the first sentence of the spell is from the in-character perspective of the spell caster:

[When you would take acid, cold, fire, lightning, or thunder damage, t]he spell captures some of the incoming energy, lessening its effect on you and storing it for your next melee attack.

What the caster knows is that the spell protects them from damage, and powers their next attack. The caster, however, doesn't have an in-character concept of rounds and game turns. That is meta-narrative, and belongs with the second part of the spell description:

You have resistance to the triggering damage type until the start of your next turn. Also, the first time you hit with a melee attack on your next turn, the target takes an extra 1d6 damage of the triggering type, and the spell ends.

This part is the mechanical effects of the spell, and it is what should be referred to by the caster's player and by the DM. As such, the spell does not contradict itself. If you attack on the same turn you cast the spell, you do not get to apply the bonus damage to your attack.

Other clear examples of this structure - first in-character narrative, then meta-narrative mechanics - can be found in the descriptions of the Lore Bard's Cutting Words feature, or the Rogue's Evasion ability.

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  • \$\begingroup\$ Your argument is convincing, but I find this "hand of the author" section unnecessary. The spells in the phb are mostly written in the way you describe, but plenty of examples aren't. Barkskin and Clarevoyance are two that I found immediately which don't conform. \$\endgroup\$ Commented May 11 at 5:16
  • \$\begingroup\$ To me, a "shadowy door" that takes you to another plane, or indeed a demiplane or another part of the material plane, can fairly convincingly be argued to be a portal, which is explicitly something that the spell prevents. \$\endgroup\$
    – Obie 2.0
    Commented May 11 at 5:36
  • \$\begingroup\$ This is the heart of the matter then. Is the shadowy door more like a planar portal or more like the opening of a bag of holding? I think it's still unclear \$\endgroup\$ Commented May 11 at 5:45
  • \$\begingroup\$ @ClericoftheWest I didn't claim that all spells were written like this. When 1 part of a spell appears to contradict another, or 1 part is too vague to interpret (like here) I think it is useful to check whether the vague part is meant to be in-character. AFA barkskin, "You touch a willing creature" That's in-character. "Until the spell ends, the target's skin has a rough, bark-like appearance, and the target's AC can't be less than 16, regardless of what kind of armor it is wearing." That's meta-narrative, and includes a reference to AC, which the player knows, but the character doesn't. \$\endgroup\$
    – Kirt
    Commented May 11 at 5:57
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    \$\begingroup\$ +1. Good answer. At first blush seems a bit long, but I probably shouldn't throw that particular rock. \$\endgroup\$
    – Jack
    Commented May 11 at 13:18
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It doesn't matter, at all

I personally hate questions like this and think even considering it is completely against the spirit of the game.

Player: I would like to protect my demiplane

DM: Hahahahahhahaa now you can't access it yourself!!! Loser!!!11!1!1

I can't imagine this being the kind of game many people want to play in. If that doesn't sound fun to you, just let it work.

If you are the DM prepping for the bad guy then it also doesn't matter. BBEGs have holes in their plans all the time, otherwise they would probably win, so protected or not you still need to give the players a way in if it matters.

Even more reasons it doesn't matter is that as a DM if you raid the players demiplane off screen then that's usually considered a dick move, so this would just be the player trying to roleplay and put some thought into it. Let them.

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  • \$\begingroup\$ I did say it was a thought experiment... \$\endgroup\$ Commented May 11 at 15:40

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