German POW castle (7)
I believe the answer is:
colditz
'german pow castle' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for colditz that I've seen before include "German wartime prison" , "German POW castle" , "Castle used as a POW camp for Allied officers, 1940-45" , "WW2 prison castle" , "Oflag IV-C" .)