Under croft

Beneath the entire Citadel of Gallifrey, there was an under croft where TARDISes were sent to die. It was a huge cave, with a high and vaulted ceiling, cut stoned walls, weakly enlightened by glowing strips in the brickwork. The floor was covered by thousands of dead or dying TARDISes, in all manner of different shapes and sizes.

During the last period of the Last Great Time War, the War Doctor and his companion Cinder adventured in it to recover the Doctor's TARDIS, sentenced to death by Rassilon. (PROSE: Engines of War)