Mario Caiano shot the film in Rome and declared it his tribute to the Gothic genre and to actress Barbara Steele.

Jenny begins having nightmares, which include the sound of beating hearts and Muriel's voice urging her to murder Stephen.

Director Mario Caiano stated that Nightmare Castle was born out of his passion for actress Barbara Steele and the Gothic genre, a style which he began to love between 1943 and '44 when he first read Edgar Allan Poe's work.

[3] The film was released in black-and-white, shot by director of photography Enzo Barboni, but it was originally planned for some scenes to be given a red tint in post production.

[1] The film was released by Allied Artists Pictures in the United States on 5 July 1966, shortly before the studio's initial demise.

[6] Nightmare Castle has been released on DVD by several companies, including Severin Films, Alpha Video and Retromedia in the United States.

"[9] In his book A History of Italian Cinema, Peter Bondanella stated that "Caiano's cinematography cannot match that of either [Riccardo] Freda or [Mario] Bava, he may well have captured Barbara Steele in even more compelling shots in Nightmare Castle than either of them did in their own, much better films.