20 Million Miles to Earth is a 1957 American science fiction film written by Bob Williams and Christopher Knopf from an original treatment by Charlott Knight. The film was produced by Charles H. Schneer's Morningside Productions for Columbia Pictures and directed by Nathan H. Juran. As with several other Schneer-Columbia collaborations, it was developed to showcase the stop-motion animation talents of Ray Harryhausen.
The government of the United States, along with The Pentagon organizes the first interplanetary expedition to the planet Venus. The spacecraft XY-21 with a crew of seventeen successfully reaches the planet 20 million miles away and vast mineral resources and precious raw materials are discovered on the planet, but atmospheric conditions are extremely harsh and cannot support life from Earth, and several members of the expedition die because of the conditions. None of this is actually seen, but is all explained in dialogue later on in the film.
On the return journey, thirteen months after leaving, the rocket is crippled by a meteor and crashes into the Mediterranean Sea off the southern coast of Sicily. The film begins as the two surviving crewmen are rescued by local fishermen before the vessel sinks beneath the waves and are taken to the local hotel. Staying at the hotel are an American scientist, Dr. Leonardo and his daughter Marisa, who is, fortunately, a medical student. Marissa tends to the crew herself, with mixed results: horribly burnt chief scientist of the expedition Dr. Sharman dies, whilst Col. Robert Calder survives. Calder determines to locate a specimen they brought with them to study how the creature survives and therefore prepare another expedition to tap into the planet's resources. In his dying breaths Dr. Sharman had different thoughts: he considered the creature a dangerous threat and beseeched Calder to find it and destroy it to prevent the creature causing destruction and carnage on Earth. Meanwhile the specimen, an egg, shrouded in jelly within a metal cylinder, washes ashore and is found by a local boy, who then sells it to Dr. Leonardo.
Overnight the egg hatches a reptilian creature, referred to as the Ymir. The Ymir begins to grow at a prodigious rate due to the abundance of oxygen in Earth's atmosphere. Dr. Leonardo thoughtfully places the Ymir in a cage. Soon, however, the Ymir becomes large and strong enough to free itself. Apparently, the Ymir eats sulfur and passes by horses, poultry and sheep before finding some bags of agricultural chemicals in a barn, one of which is sulfur and begins to eat. The Ymir only attacks when provoked and after being attacked by a dog and a farmer it escapes the barn. This time the Ymir runs to the erupting volcanic crater at Mount Etna.
It is found by the Italian army and American army only to be chased into a trap. However by this point the Ymir has grown over 20 ft high. The army ensnare the Ymir in an electric net and it is and transported to a zoo in Rome. Believing the situation is over, and themselves safe at last, Calder and Marissa begin to develop a romantic relationship.
After studying the Ymir for some time, something goes wrong in the zoo's laboratory when an accident disrupts the flow of electricity. The Ymir escapes and is attacked by an elephant. The Ymir, victorious after the battle, then goes on a rampage, smashing through buildings. Calder chases the Ymir down to the Tiber River in Rome, which promptly resurfaces and begins to attack the human threat and smashes through the bridge. Firearms are little use against the Ymir.
The Ymir, after being shot at by powerful explosive rockets, ends up on top of the Colosseum. After tearing into the brickwork and throwing pieces down at people and soldiers, it is eventually shot down by an intense barrage of rockets and falls some fifty meters, whereby it is crushed by falling masonry. The film ends with scientist Dr. Judson Uhl, played by John Zaremba, looking over the dead body of the Ymir and saying "Why is it always, always so costly for man to move from the present to the future?"