Nineveh

Nineveh was a place to which the Seventh Doctor was once diverted. It was, in his words, a kind of "null space" devoid of even stars. Whether it was a planet, asteroid or even another dimension was unclear. However, it was definitely the final resting place for an entire junkyard of TARDISes. It was also the place where any number of Time Lords met their end. Indeed, the Seventh Doctor himself very nearly was killed there by the region's master, the Watcher of Nineveh. (COMIC: Nineveh!)

Behind the scenes
In the real world, there existed an ancient Assyrian city.