D&D 5E What demiplanes have been described in D&D? Inspiration for Acererak's phylactery location

[Quickleaf]

There's the Demiplane of Moil from Return to the Tomb of Horrors. That adventure also has Acererak's lair – the Fortress of Conclusion on the Negative Energy Plane.

I hinted at the end of my own game that Acererak's lair / phylactery was located in the Demiplane called Dungeonland, based on the Alice in Wonderland inspired Gygax novel of the same name.

You can also read about several other demiplanes here: Demiplane - 1d4chan

 

[MonsterEnvy]

Yeah Acererak can pretty much do what he wants with his Demiplane. He's likely warded his Phylactery against pretty much everything. Without his help it would be nearly impossible to find it. If I recall his Phylactery in Return to the Tome of Horrors is in a dungeon located inside a vacuum with Negative energy running through everything. Lots of stuff to murder people that come in, and hidden behind many tricks with several false areas, and treasures to make you feel you completed it.