Colditz Castle... not as pretty as Gabriella imagined...
Many books and movies have told the stories of the brave escape attempts from Colditz
In The Obsidian Mask, Alex mentions Colditz Castle when he tries to cheer up Lorenzo, Gabriella and Natasha in the cave. He tells them about the brave officers who were captured during World War 11 and were held there as prisoners of war in the large, austere castle that the Nazi's used as a high security prison. Many ingenious escapes were conjured up and attempted by these brave men but only a few of those men actually made it home, or even further than a few miles from the town surrounding the castle.
Without giving too much away, if you haven't read The Obsidian mask yet, Alex's telling a little of the Colditz story when they were held captive, gave Gabriella the encouragement to be brave enough to do what needed to be done when, he and Lorenzo couldn't.
Forged I.D papers and passports were made by some prisoners to help others planning their escape attempts. Some groups were to make the clothing, wigs etc. Others were in charge of the fake papers the escapees would need. One prisoner hid in a suite case, another dressed as a woman, some dug under the castle... but very few men made it out alive. There are many books on Colditz and the escapes attempted. They are well worth looking up.