Baron Blood

Baron Otto von Kleist

Eva Arnold

Dr. Karl Hummel

Peter Kleist

Inspector (as Humi Raho)

Fritz (as Alan Collins)

Mayor Dortmundt

Madeleine, the doctor's assistant (uncredited)

Dr. Werner Hessler (uncredited)

Gretchen Hummel (uncredited)

Auctioner (uncredited)

Man on the aircraft (uncredited)

Woman on the aircraft (uncredited)

Land surveyor (uncredited)

Martha Hummel (uncredited)

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.

The Vienna castle that the film was shot at was actually a museum that was filled with valuable antiques; among them a chair valued at a half a million dollars.

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.

Eva's hairstyle markedly changes in a matter of minutes: from the dinner scene at Karl's house to just a few minutes later when she and Peter are inside the castle, her hair goes from a wavy perm to being nearly straight-combed.

When Peter comes to Eva's rescue at the castle, it is clearly broad daylight. Eva begs Peter to take her home, which he does, but now as we see him drive up to her student dorm, it is pitch black outside.

At the airport the uniformed airline employee greeting passengers at the base of the portable stairway suddenly disappears between shots.