Altrazar

 was a legendary city that was lost in time. Romana II described it as a temporal Atlantis and a cautionary tale for Time Tots. It was lost as a way for the Time Lords to hide a Blinovitch Limitation Effect limiter when the former inhabitants used the device to rewrite their own past multiple times. The Time Lords couldn't do anything to stop this without rewriting history. A gang was using it as a bolt hole to hide information. (AUDIO: The Trouble with Drax)