Since Sir Christopher Lee was cast at the last minute, he decided to bring along his own wardrobe: the smoking jacket he had worn as Sherlock Holmes in Sherlock Holmes and the Deadly Necklace (1962)
Sir Christopher Lee claims he had no idea this was softcore porn until he actually saw the movie. Various of his scenes were shot, and then edited in with the sex scenes later and during the opening sequence, he was unaware there was a nude woman on the altar behind him, because drapery was swirled over her as soon as the camera stopped rolling and he'd turn around.
The part played by Sir Christopher Lee was originally offered to George Sanders, who withdrew through illness.
The song in Spanish that the characters sing in the boat about 1 hour and 5 minutes into the movie, and which then segues into an instrumental arrangement of itself, is "Vamos a la cama", a very well known TV jingle from 1960s Spain that was aired every day as a short cartoon starring a family of six kids known as "La familia Telerín" with the purpose of sending kids to bed when children's TV slot ended. The film's version has changed lyrics.