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.
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.
One day, the police in the German town where this movie was shot set up a speed trap near the set. Several members of the cast and crew were caught, including Steve McQueen. The Chief of Police told McQueen "Herr McQueen, we have caught several of your comrades today, but you have won the prize (for the highest speeding)." McQueen was arrested and briefly jailed.
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.