Julius Castle, a restaurant with a castle-like exterior located on San Francisco's Telegraph Hill, was used as the exterior of the house in the film. The filmmakers built a mansion-like exterior around parts of the restaurant to hide certain elements (such as the "Julius Castle" sign on the outside wall). Built in 1922, Julius Castle served as a high-class restaurant until it closed in 2008. (It is currently for sale.)
The grocery store where Tony worked was an actual store called Speedy's. It was open 94 years from 1914 to 2008 at 301 Union Street San Francisco, CA 94133. Google Maps Streetview shows that the corner store building still looks similar to the movie.
Thr role of the real Karin Dernakova in the concentration camp was played by Natasha Lytyss who just a few years later was employed by Marilyn Monroe as her first on and off set drama coach until being replaced be Actors Studio guru Lee Strasberg and his wife Paula, who served as on set coach in the last 6 Monroe films.
The portrait shown throughout the movie as "Aunt Sophie", was a painting of actress Helena Benda.
Other actors considered for the Richard Basehart role include James Mason, Hugh Marlowe, Richard Widmark, Dana Andrews, John Lund, and Richard Conte.
Other actresses considered for the Fay Baker role of Margaret include Andrea King, Jayne Meadows, Audrey Totter, Nancy Reagan, Mercedes McCambridge, Marsha Hunt, Ann Savage, and Uta Hagen.