Served as a pilot film for the anthology TV series, _"Ghost Story" (1972) which changed it's title to "Circle of Fear" in 1973.
Director John Llewellyn Moxey and writer Richard Matheson were the same team responsible for the popular TV movie The Night Stalker (1972).
Included on The William Castle Film Collection, DVD set, as a special feature behind Mr. Sardonicus (1961).
The fictional hotel in this series, "Mansfield House", where hotelier-narrator Winston Essex (played by Sebastian Cabot) presents the story in the opening scene, is actually Hotel Del Coronado in San Diego. It's an historic landmark built in 1888; many presidents, celebrities, authors, etc., having stayed and/or worked within its walls. It remains a busy, upscale beachfront resort. Some Like It Hot with Marilyn Monroe, Tony Curtis, and Jack Lemmon was filmed at "Hotel Del".