Gallifreyan sarcophagi were hibernation units used by Time Lords.
The Seventh Doctor once used a Gallifreyan sarcophagus after he trapped Nobody No-One in his mind. The Forge kept the sarcophagus in the archive of the Crichton Building. After a large portion of London was destroyed by a bomb, Ace and a younger version of the Seventh Doctor found the sarcophagus and released the older Doctor and Nobody. (AUDIO: A Death in the Family)
