Planet (The Velvet Dark)

The Master was exiled to a planet by the Time Lords after they stripped his body from him, leaving him as only darkness maintained by his will.

The planet had a forest with a castle, where the Master was intended to live out his meager existence, before his TARDIS found him and created the Watcher Master, jumping between the planet and Earth in order to lure the Fifth Doctor and steal one of his future regenerations. (PROSE: The Velvet Dark)