Medusa Cascade

The Medusa Cascade was a colourful nebular region of space and the location of a rift in time and space which was sealed at some point by the Doctor.

It was located "halfway across" the universe from Earth. (TV: The Battle of Ranskoor Av Kolos)

Appearance
The Cascade was nebulous in appearance, containing what appeared to be clouds of coloured gas. (TV: The Stolen Earth) In addition to the space-time rift at its heart, (TV: Journey's End) it also contained at least fifteen "broken moons". (TV: The Sontaran Stratagem)

History
The Medusa Cascade was visited by the Doctor in his first incarnation when he was "just a kid" of ninety years old. (TV: The Stolen Earth), where he sealed the rift as part of his practical temporal technology exam. (PROSE: Report on Term's Work) The Fourth Doctor and Romana later visited it. (PROSE: City of Death)

In one potential timeline of the Last Great Time War, Livia and Narvin saw the Medusa Cascade burn to nothing as a result of becoming creator of the Daleks. (AUDIO: The Master's Dalek Plan)

The Medusa Cascade was the place to which Davros's New Dalek Empire moved twenty-seven planets. The planets could not be found by regular means, as they were out of temporal synchronisation with the rest of the universe by one second. (TV: The Stolen Earth) Davros placed them there so that when his reality bomb was set off, it could penetrate the Cascade's space-time rift and spread the bomb's destructive force across every possible timeline and all of existence. (TV: Journey's End)

This act led to an invasion of Earth, one of the required twenty-seven planets. (TV: The Stolen Earth) It ended with the near-total destruction of the Daleks by the Meta-Crisis Tenth Doctor and (with the help of the Doctor and his companions) the return of all of the planets to their correct locations in time and space. (TV: Journey's End)