The Unknown Terror is a 1957 black and white widescreen American science fiction/horror film directed by Charles Marquis Warren and starring John Howard, Mala Powers, Paul Richards and May Wynn. It was produced by Robert Stabler. The narrative follows a group of explorers who, while searching for a missing man, come across the "Cave of the Dead", filled with parasitic fungi and inhabited by foamy, fungus-covered monster men. The film was released theatrically in the US in August 1957 on a double bill with Back from the Dead.