Sometime around 1997, there emerged a massive Internet hoax which claimed that a Siberian borehole had penetrated the Earth's crust into Hell itself, with "proof" being an audio recording of the screaming souls of the damned. This urban legend (variously known as the "Siberian Sounds of Hell" or "The Well to Hell" hoax) featured in many tabloids, and was even cited by some Christian groups as hard proof of a real Hell. The sound effects supposedly recorded within the borehole were actually a combination of story elements from a radio broadcast "Quiet Please - The Fourble Board", and audio lifted from this film.
Originally director Mario Bava didn't want to shoot the film outside of Italy but after producer Alfred Leone found the castle location in Vienna, Austria Bava decided it was a perfect setting for the film.
At first Vincent Price was approached to star in the production but Price declined. Then Ray Milland was considered, however Milland was unable to travel to the shoot. Finally veteran actor Joseph Cotton was suggested and to Bava's surprise Cotton accepted the role.
The Vienna castle where the film was shot was originally thought to be a museum, but that information is incorrect. In his book "Mario Bava: All the Colors of the Dark," Tim Lucas gives this misinformation, but on commentary of the Kino-Lorber DVD release he corrects himself, explaining that the film's producer had stated that it was filmed at the museum. Lucas had, since the book's publication, learned that it was actually shot at Burg Kreuzenstein.