Aye young lad, reminds me of the time I was at Colditz Castle many years ago.
Plotting my escape
Digging a tunnel
Just walked out the front door in the end
As mentioned earlier, Mohne and Eder Dam are worth a visit also. Especially the Eder, imagining them fly over the hill by the castle in the dark, swoop down to 60 feet, then missing the hill after the dam. Riding away after following the river downstream also brought it home what it must have been like for the locals.
ps I think you can stay overnight at Colditz now. When I was there they were 1/2 way through doing it up and restoring it.