Colditz Castle
Damn Interesting (which is a pretty damn interesting blog) has a good article on Colditz Castle and various escapes attempted by Allied forces being held as prisoners of war.
The structure looked extremely formidable. It was situated on a rocky outcropping. The outer courtyard housed the 200 or so Germans it took to maintain the place and the inner courtyard was used by the prisoners. The outer courtyard had two exits. One led over the moat into the town, the other into the forest. The prisoner side was lined with a 100 foot cliff into a river. Although this seemed terribly impregnable, one German officer mentioned, “…apart from putting bars on the windows, it had never really been built for he purpose of keeping people in. A more unsuitable place to hold prisoners will probably never again be chosen.” As with similar structures, the place was a labyrinth of tunnels and passageways, perfect for escaping “bad boys”. Still it wasn’t all tea and crumpets. Before the influx of Red Cross packages, they were literally starving.