Rassilon's Foundry

Rassilon's Foundry was an ancient stronghold of the Time Lord Rassilon where he worked on his technological secrets during the distant past of the planet Gallifrey.

It was a secret hiding place located in the wastelands and protected, along with a reality lock, by a one second time shift into the future. The Foundry made use of dimensional technology, making it larger on the inside than it appeared externally. Within its chamber, Rassilon tampered with Gallifreyan physiology in order to give them life after death, a secret that at the time only the Vampires possessed.

The Foundry contained many technological wonders that were later used by the Time Lords, from a statue of Nemesis to the De-mat Gun. There were even star systems trapped within the structure, home to civilizations that Rassilon felt were a threat to him and included the Divergence. (BFA: Zagreus)