The real camp can be visited today in Sagan, Poland. It's a ruin now, that's mostly used for archaeological purpose. A replica of the camp is located forty kilometers (twenty-five miles) south, where you can enter a model of tunnel "Harry" yourself. In the movie, they confused the actual names of the tunnels.
Charles Bronson, who portrays the chief tunneler, brought his own expertise and experiences to the set. He had been a coal miner before turning to acting, and gave director John Sturges advice on how to move the dirt. As a result of his work in the coal mines, Bronson suffered from claustrophobia, just as his character had.
Wally Floody, the real-life "Tunnel King" (he was transferred to another camp just before the escape), served as a consultant to the filmmakers, almost full-time, for more than a year.
In this movie, several Americans (including Hilts and Henley) were amongst the escapees. In real life, American officers assisted with the construction of the escape tunnel, but weren't amongst the escapees, because the Germans moved them to a remote compound just before the escape.
Several cast members were actual POWs during World War II. Donald Pleasence was held in the German camp Stalag Luft I, Hannes Messemer in a Russian camp, and Til Kiwe and Hans Reiser were prisoners of the Americans. Pleasence said the set was a very accurate representation of a POW camp.