The Beast from 20,000 Fathoms is a 1953 American science fiction monster film directed by Eugène Lourié, with special effects by Ray Harryhausen. The film stars Paul Christian, Paula Raymond, Cecil Kellaway, and Kenneth Tobey. The screenplay is based on Ray Bradbury's 1951 short story "The Fog Horn", specifically the scene where a lighthouse is destroyed by the title character. The film is about the Rhedosaurus, a dinosaur that is released from its frozen hibernating state by an atomic bomb test in the Arctic Circle and begins to wreak a path of destruction as it travels southward, eventually arriving at its ancient spawning grounds, which includes New York City.

Plot

Far north of the Arctic Circle, a nuclear bomb test, dubbed "Operation Experiment", is conducted. Prophetically, right after the blast, physicist Thomas Nesbitt muses "What the cumulative effects of all these atomic explosions and tests will be, only time will tell". The explosion awakens a long carnivorous dinosaur known as a Rhedosaurus, thawing it out of the ice where it had been held in suspended animation for millions of years. Nesbitt is the only surviving witness to the beast's awakening and later is dismissed out-of-hand as being delirious at the time of his sighting. Despite the skepticism, he persists, knowing what he saw.