Homeplanet of Time Lords. It was located in the constellation of Kasterborus, 29,000 light years away from Earth. Gallifrey was the location of the Trial of the Second Doctor, and was briefly invaded by the War Lords (ZZ). Later, it was almost destroyed during the Omega crisis, but was saved by the Three Doctors (RRR). It was threatened by the Master when he almost released the Eye of Harmony (4P). It was then invaded by the Vardans and the Sontarans (4Z). In both cases, Gallifrey was saved by the Fourth Doctor. The Fifth Doctor was tried on Gallifrey when Omega threatened to take over his body (6E). Finally, Borusa brought the Five Doctors to Gallifrey's Death Zone to help him unlock the secret of the Tomb of Rassilon (6K).
Gallifrey was protected by impenetrable force fields known as transduction barriers. It was the location of the Capitol, the Time Lords' seat of power. A great deal of the surface of the planet was barren and wild, and inhabited by the Shobogans (or Outsiders) (4Z). The Death Zone was a forbidden area, protected by force fields, at the center of which was the Tomb of Rassilon, known as the Dark Tower (6K). The Third Doctor once mentioned that he lived on a mountainside in South Gallifrey (OOO). (The name of Gallifrey was first mentioned by the Third Doctor when he was interrogated by Linx (UUU).)