Zanak

Zanak was a hollow planet which, using powerful engines, could materialise around other planets and steal their mineral wealth. It would finally crush the planets into compressed cores small enough to carry. The surface was pleasant, with green fields, lush vegetation and friendly, Near-human natives.

Not a native of that world, the cyborg space pirate known as the Captain ruled from a mountain fortress known as the Bridge. He, in turn, answered to Queen Xanxia, who had recreated him in his current form after his ship had crashed on Zanak in the distant past. Xanxia had gutted her entire planet to provide the power needed to control the time dams that kept her body frozen in its last few seconds of life while she projected her consciousness into a new, virtually-generated body.

The Fourth Doctor visited Zanak and helped the Mentiads overthrow both the Captain and Xanxia. The Bridge was destroyed, allowing Zanak to settle in the position that had once been occupied by the planet Calufrax, its interior mass replaced by the remnants of the planets that Zanak had destroyed and the Captain had preserved as part of a plan to destroy Xanxia (With the exception of Calufrax, which had been the second segment of the Key to Time). (DW: The Pirate Planet)