After a young man is killed in an unexplored subterranean cavern and his girlfriend driven mad by something she saw there, a track found at the scene cannot be identified with any known animal and thus a scientific expedition is launched to find out just what it is that is living there.
Practical Effects
Gloriously unconvincing monster suits that demand respect.
Production
Cave sets built on obvious soundstages with dramatic shadows.

Director
Alfredo B. Crevenna
Trivia, insights & behind the scenes
Part of Mexico's 1960s horror boom, when local studios raced to create their own Universal Monsters equivalent on shoestring budgets.
Director Crevenna later became known for Santo wrestling films; you can see him practicing the same costumed chaos here.
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