Can you Dispel a Demiplane?

Question

After reading the answers to this question and attempting to answer this question, I got to thinking about the nature of planes created by the spell demiplane. The part of the spell that especially got me thinking is the following :

Each time you cast this spell, you can create a new demiplane, or have the shadowy door connect to a demiplane you created with a previous casting of this 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.

This text implies that the spell either creates a new demiplane, or allows access to a demiplane that was created by this spell. As such, could one of those demiplanes be targeted by a spell such as dispel magic, as an "effect" of the spell demiplane? What about suppressing some or all of a demiplane, such as using an antimagic field?

This question could also extend to demiplane-like extradimensional spaces created by magic items, such as a bag of holding or a portable hole, since they are of a similar nature. As for what would happen if the dispel worked, at least for those it would seem logical to conclude that their contents are scattered across the astral plane, just like when they are destroyed, but I could be wrongly assuming that the result would be the same.

Answer 1

You cannot dispel a demiplane, only its door

Demiplane states:

Each time you cast this spell, you can create a new demiplane, or have the shadowy door connect to a demiplane you created with a previous casting of this spell.

Once the demiplane is created, it itself is not a magical effect any more. The Sage Advice compendium explains this:

Can you use dispel magic on the creations of a spell like animate dead or affect those creations with antimagic field? Whenever you wonder whether a spell’s effects can be dispelled or suspended, you need to answer one question: is the spell’s duration instantaneous? If the answer is yes, there is nothing to dispel or suspend. Here’s why: the effects of an instantaneous spell are brought into being by magic, but the effects aren’t sustained by magic (see PH, 203).

While the duration of the demiplane spell itself is not instantaneous, the creation of the demiplane is. If its existence were sustained by the spell's magic after creation, it would need to vanish when the duration of the demiplane spell expires, and anything you put there would be lost forever. This is not the case.

The fact that you can connect to the same demiplane you created long afterwards makes it clear that the original casting instantaneously creates something that is being brought into being by magic, but not later sustained by magic, and this means it cannot be dispelled later on.

You can dispel the ongoing magical effects of demiplane that persist only during the duration of the spell. This means, you could dispel the door that leads to the demiplane.

The same reasoning applies to antimagic field: it will not end the demiplane, but can remove the door.

About the walls...

In my question about the nature of the demiplane's walls, one of the answers claims that a demiplane's walls are "made out of magic". I do not think they really are in the sense that they would be suppressed by an antimagic field or could dispelled. They are part of the demiplane, and therefore unaffected.

What exactly the walls are made of is unclear to me. Maybe the fabric of reality of the demiplane. I agree with the reasoning that they are not actual wood or stone.

If they could be suppressed, this would not alter the dimensions of the demiplane, it still would be a 30 foot cube, you just would not have visible walls then anymore, and this would raise its own questions of how the walls look like or what you would see, if anything. I think it's even likely that avoiding these questions is the reason why the spell description says the walls appear to be stone or wood.

Answer 2

Dispel Magic will not destroy the demiplane

Dispel Magic can only target a creature, an object or a magical effect - the demiplane is none of those.

Answer 3

My interpretation is that Dispel Magic would only get rid of the door, not the entire demiplane

Granted, the wording of the spell is somewhat hazy in this regard but this is what my interpretation is based on: First off, the Demiplane spell states:

You create a shadowy door on a flat solid surface that you can see within range. (...)

So the spell only creates a door to the demiplane, not the entire demiplane itself. This door is then what can be the target of Dispel Magic. The demiplane might be created as part of the spell to get it to work but it doesn't have to be, you can also have the door connect to a demiplane already existing.

It does state later on in the the description that:

Each time you cast this spell, you can create a new demiplane, or have the shadowy door connect to a demiplane you created with a previous casting of this spell.

This is somewhat contradictory but my interpretation of this is that the creating of the demiplane is just a side effect and creation of the door is the primary aim of the spell, i.e. you can't create a door to a non-existent demiplane.

Furthermore, the Demiplane spell also states:

When the spell ends, the door disappears, and any creatures or objects inside the demiplane remain trapped there, as the door also disappears from the other side.

So the demiplane persists after the spell ends, the only effect is that the door itself disappears. The effect of Dispel Magic is causing the spell being dispelled to end:

Any spell (…) on the target ends.

Regarding Antimagic Field, I am not sure how it would interact with Demiplane but my guess it that it would also only suppress the door itself as well. There's also the Sage Advice Compendium piece that Groody's answer addresses already so I'm not going to duplicate it but it explains this in more details. Basically, the demiplane is something that gets created as part of the spell but then exists on its own, disjoined from the spell. Therefore, it cannot be either dispelled or suppressed.

About effects created by magic items, there's already a separate question about this and the answers explain why you can't Dispel Magic an item, Antimagic Field would suppress their magical properties though. The spell gives example of a sword:

Magic Items. The properties and powers of magic items are suppressed in the sphere. For example, a +1 longsword in the sphere functions as a nonmagical longsword.

This is clearly meant to extend to other items so I would say that e.g. a Bag of Holding becomes a regular bag while in the Antimagic Field.

Answer 4

My take on this is that it will not destroy the demiplane, but the doorway can be dispelled. The spell last for 1 hour so there must be something to dispel since dispel magic has a chance to end all non-instant spell effects.

Here I refer to the Dispel Magic, it says

Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends.

The important part is that the spell ends. So what happens to the demiplane would be

When the spell ends, the door disappears, and any creatures or objects inside the demiplane remain trapped there, as the door also disappears from the other side.

So you have exactly what will happen when you make a successful ability check after casting dispel magic. The door is dispelled and the demiplane stays there.