First, he addressed the part of prison escape that every other escapee forgets--what you'll do once you're outside the walls. The prison was right there in Germany, after all, and he didn't even know the language. So, he convinced his captors to start classes in how to learn German.
Next, he needed to coordinate with somebody on the outside. His letters to and from his wife were read and censored by the guards, but they somehow developed a system of embedding coded messages that the captors never picked up on. Next, he got ahold of a map and memorized every detail of the surrounding geography.
All right, now there's just the matter of the, uh, 150-foot drop outside the prison walls that had made escape utterly impossible for the last eight centuries.
He and a friend came up with some twine, thin stuff like they use to bind packages. They twisted it together, bit by bit, until they had 150 feet of it. It took a year.
Last, he got himself a Tyrolean hat.
Together, these preparations helped Giraud pull it off. Link -via Gorilla Mask