Quinnis

Quinnis was a planet located in the fourth universe (although once the Doctor said it was in Galaxy 4). It had at least one moon, Ronnos, which was used as a prison colony.

The First Doctor and Susan nearly lost the TARDIS during a visit to Quinnis the trip before their visit to 1963 London. (DW: "The Edge of Destruction", CC: Quinnis) The planet had a purple sea. (DWY: A Religious Experience)

The Quinnis criminal Roztoq used the TARDIS to escape to the Doctor's native universe and arrived in 1909 England, where he posed as the Marquis of Rostock until the Doctor captured him and returned him to the fourth universe. (ST: 64 Carlysle Street)

The Doctor claimed to have trained as a ninja on Quinnis. (PDA: The Devil Goblins from Neptune)