Colditz Castle was a castle, located near Leipzig, in Germany. It was used as a prisoner of war camp by the Nazis during World War II, during which time it was known as Oflag IV-C.
In 1942, the castle was mentioned by Winston Churchill in the Ninth Doctor's presence. The Doctor recalled visiting the castle. (AUDIO: I Was Churchill's Double)
It was visited by the Seventh Doctor and Ace in October 1944 and by Elizabeth Klein from an alternate 1965 in which the Nazis won the war. (AUDIO: Colditz)