Mictlan

Mictlan was the extra-dimensional home of the Celestis, who created it after their migration from the Homeworld. It served as a metaphysical bomb shelter removed from spacetime. It made its occupants immune to time winds or changes imposed on Gallifrey's past. (PROSE: The Taking of Planet 5) The appearance of this realm varied with the perceptions of its inhabitants. (PROSE: Alien Bodies) It was created by the use of block-transfer engines and computational matrices which also linked all the Lord Celestials who made up the Last Parliament.
The Celestis took those close to death to Mictlan. (PROSE: Autumn Mist) As a result, many viewed it as a form of hell. (PROSE: The Book of the War) The Bone Museum of Mictlan served as a library for agents of the Celestis. It held information on the Doctor. In addition, the Plain of Bones was located in this realm.
It was destroyed due to the actions of a renegade Celesti, the Hermit, and the Fendahl Predator. (PROSE: The Taking of Planet 5)
== Behind the scenes ==
* Mictlan was the name of the Aztec underworld.