Escape from [Demiplane]

[Thalandar]

So the other day I was surfing channels and I came across the old Escape from New York movie.

It got me thinking about Ravenloft, and demiplanes, and the Donjon card of the Deck of Many Things, and even the Holodeck episodes of Star Trek Next Generation.

In a fanatasy world, were powerful wizards and magics are the norm, and lawful good idealists balk at execution, what about a demi-plane prison to house all your BBEG if they are captured?

As far as the Deck of Many Things goes, my thoughts were this:
It is an artifact. Someone created it, perhaps they too created this demiplane, and the demi-plane is were you go when you draw the dungeon card. And in fact, you don't know it, because it seems like the real world. IDK, thoughts?

[Protoman]

Check out the (Greater) Create Demiplane spell.

First, make a suitably large demiplane and make permanent (However big you want, I assume you're dm so cost isn't an issue. If player, whatever you feel like affording).

Second, make a portal 50 ft in the air or wherever that may be hard to get to without magic. Block up the portal with an adamantine door or something.

Next, give the demiplane the dead magic trait. Important to make the portal first or the demiplane is pretty much pointless.

Next time you have a prisoner, throw him into your own personal Phantom Zone (DC Comics) or Prison 42 (Marvel Comics). Maybe have decent golems guarding the door and patrolling the demiplane grounds.

[Goth Guru]

Welcome to the hotel California. The golems are nightmen. Weapons do no damage"They stab it with their steally knives, but they just can't kill the beast!" Illusions might work, but all damaging or plane shifting spells fail. While there there is no access to the planes of Shadow, Etherial, or Astral.