Tomb of Rassilon
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This is the tomb of Rassilon, where Rassilon lies in eternal sleep.
The Tomb of Rassilon, also known as the Tower of Rassilon or the Dark Tower, was a large tower in the Death Zone on Gallifrey.
The tower contained a crypt where supposedly resided the physical remains of Rassilon. It had three entrances: a front entrance, a door on the roof, and access from caves below.
There were a variety of obstacles and boobytraps which made the journey into the tower complicated. (DW: The Five Doctors)