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The Unknown Terror is a 1957 widescreen American horror science fiction 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.