Couple of years ago I realised one of life's ambitions and visited Stalag Luft 3 and Colditz.
Started in Poznan and visited the War cemetery at the Citadel. Gravestones of 25 of the 50 are there though I believe Roger Bushell's Urn broke and his ashes are actually scattered at Zagan. Quite a number of graves in groups of 5 or 7 and obviously complete crews.
Then went to Zagan and the remains of the camp. There is a visitor centre about a mile away with hut and tower reconstructions as well as a tunnel section with Perspex roof you are able to try for yourself. The camp itself is eerily quiet and you cannot appreciate the size of the camp and huts unless you are there. The Watchtower is new since I was there. The memorial built by the prisoners is next to a cemetery for a Polish conflict of 18?? so has either been relocated or the camp is even bigger than I thought.
Then went to Colditz, and considering it was behind the Iron Curtain when the film was made it was like I knew every wall window and doorway. Following Pat Reid's footsteps was uncanny. I believe I was there just before they recreated the glider and flew it off the roof.
Cynicalint
You're right about what didn't happen but I always thought James Garner's scrounger was based on Sqn Ldr Jimmy James. And the motorbike was a Triumph, possibly Steve McQueen's own.