Under croft

Beneath the Citadel on Gallifrey, stretching across its entire area, 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 who wanted to keep the Doctor and Cinder trapped on Gallifrey so then the plan to close the Tantalus Eye to stop the Daleks plan to erase Gallifrey's history from the universe was not prevented. (PROSE: Engines of War)