Colditz was the last stop for prisoners of war in the Second World War. It was to this impregnable fortress that the Germans sent all those prisoners who persisted in escaping from other camps, such as Stalag Luft III (of THE GREAT ESCAPE FAME). Once within the walls of Colditz, the Germans reasoned, escape was impossible. And yet during the four-year period when the castle was used as a prison over 300 men escaped, 31…