Demiplanes are ill-defined planes of unusually small size that lie either within other planes or outside the known planes depending on which cosmological model you are using. Demiplanes are typically, if not always, of finite size.

  • In the Great Wheel cosmology, demiplanes were found in the Ethereal plane because they were formed from the swirling proto-matter that made up the Ethereal.[1] The Demiplane of Shadow was the best known example and still exists in some form today.
  • In the World Tree cosmology there were a few demiplanes that were part of astral dominions[2] such as the demiplane of Sildëyuir.[3]
  • In the World Axis cosmology demiplanes can exist within other planes or outside of either the parallel planes or the fundamental planes. There are undoubtedly several of them, but most are unknown. Aside from those that lay within the dominions of the gods the best known is Sigil, also called the City of Doors, which acts as a strange interplanar nexus with hidden doors to every known plane—and many that remain largely unknown.[4]