The movie takes place on Pellucidar, a fictional Hollow Earth invented by Edgar Rice Burroughs for a series of action adventure stories.
The last film produced by Amicus, Hammer's chief rival during the 1960's and 70's. Filmed January 20-March 1976, on the heels of Hammer's final horror feature "Una hija para el diablo (1976)."
The film opened on Edgar Rice Burroughs's birthday, 1 Sep, in theaters and drive-ins throughout Southern California.
This film was riffed on Mystery Science Theater 3000 - The Return (season 1, episode 14, 2017).