The Morass (The Crimson Hand)

The Morass was an alternate dimension that resembled a red vortex, and was where the Manus Maleficus originatd from. According to the Doctor, time and space in the Morass had been torn apart, leaving only the Reapers and the Chronovores.

After Majenta Pryce used the Manus Maleficus to destroy the Crimson Hand, the Manus returned to the Morass. The Tenth Doctor briefly entered the Morass with the Manus, before he used it to save Majenta. (COMIC: The Crimson Hand)