The "Time" magazine that Irving Lambert is reading on the bed just before he is attacked is the 6/22/70, edition (cover: 'Middle East in Turmoil').
Lead actress Soledad Miranda was killed in a car accident in Portugal soon after finishing this film. She was director Jesús Franco's favorite leading lady and he was planning on starring her in his next film, Female Vampire (1973). After she died, he discovered and cast Lina Romay, who went on to appear in 100 of his films and married him in 2008.
Based on the short story "Keepers of the Stone" in the collection "Sanders of the River" by Edgar Wallace and forming a part of exotic stories on the fictional indigenous people of the Akasava. It is a late example of Wallace film adaptations that were particularly popular in Germany during the 1960s.
One of a batch of films Jesús Franco made for German producer Artur Brauner in 1971 and 1972. Ladislas Fodor, a regular writer for Brauner, also had a hand in the script.