The stoyline concerns the events leading up to the total destruction of the ancient continent of Atlantis during the time of Ancient Greece.
A Greek fisherman named Demetrios (Sal Ponti, under the screen name of Anthony Hall) and his father rescue Princess Antillia (Joyce Taylor) from a shipwreck without knowing that she is from the technologically advanced civilization of Atlantis. After rescuing the princess, Demetrios must travel beyond the Pillars of Hercules to take her home. After they are picked up at sea near Atlantis by a giant fish-like submarine boat, Demetrios, expecting to receive a reward for returning Antillia, is instead enslaved and forced to work in the crater of the volcano that dominates the center of the continent.
King Cronus (Edgar Stehli) is being manipulated by an ambitious usurper, Zaren (John Dall), collaborating with the court sorcerer, Sonoy the Astrologer (Frank DeKova), who wishes to use the resources of Atlantis in order to conquer the known world. From the continent's volcano, the slaves of Atlantis have been mining unique power crystals which absorb the sun's rays and can then be used to fire heat ray beams. The crystals were originally used to produce light and heat, but due to its arrogance, corruption, and moral laxity, Atlantis has made the crystals into a deadly heat ray weapon (similar to a modern-day laser beam), and has now become "an abomination before Heaven".
Taken to the House of Fear, where a mad scientist (Berry Kroeger) turns slaves into beasts, Demetrios is saved by being given the chance to undergo the 'ordeal of fire and water'. He fights with a giant ogre in a pit of burning coals. Demetrios outmaneuvers his clumsy opponent, setting fire to the ogre's hair, the fight contrasting with the uproarious laughter coming from the massive crowd in the coliseum, cheering on the spectacle. Later, after killing the ogre in a rising pool of water, Demetrios is declared a free citizen of Atlantis.
Impending doom hangs heavy in the air of Atlantis. The birds, animals, and even the insects are fleeing what appears to be the coming destruction of the continent. With the help of a kindly high priest named Azar (Edward Platt), who explains these signs of apocalypse to him, Demetrios is later able to rescue Princess Antillia after he has helped the slaves of Atlantis to escape the coming destruction.
The skies darken, the ground begins to shake, and the destruction of Atlantis begins, just as Zaren's giant crystal ray weapon is fired by him on the fleeing citizens, as he tries to destroy Demetrios and Princess Antillia struggling to escape through the fleeing multitude. The volcano undergoes a cataclysmic eruption. As the continent proceeds to tear itself apart, the people of Atlantis panic, striving without success to escape their doom. Azar and Zaren wrestle after Azar is able to stab him with Zaren's own knife. The large crystal ray weapon swings back and forth, out of control, firing at random, until it suddenly incinerates them both. As lightning flashes and thunder roars, the entire continent is sinking just before it begins to rise up quickly. Just as quickly the sea bottom collapses, and Atlantis plunges beneath the waves. The large crystal atop the capital's large pyramid, the main power source for the entire continent, short-circuits, and a massive explosion follows.
The skies suddenly clear. Various groups of survivors, including Demetrios and Antillia, flee to Greece and other parts of the world, where they are absorbed into other cultures, and the Legend of Lost Atlantis is spread through the many peoples and nations that follow through the centuries.
George Pal originally wanted Italian sword and sandal actor Fabrizio Mioni, best known for his portrayal of Jason in Hercules as the lead, but his work visa expired and he had to leave the U. S. Other actors considered were Richard Chamberlain and William Shatner. The film had several sequences filmed off Santa Catalina Island, California.
The film is notorious for its inclusion of stock footage from other films, including the Oscar-winning Quo Vadis and The Naked Jungle. Props from other film productions were also reused, including the large temple idol from The Prodigal, Krell instrument gauges from Forbidden Planet, and wardrobes from Diane and Ben-Hur. When pointed out to George Pal that there were thousands of years of difference between the various costumes and props, he replied "Who knows"?
The spectacular special effects work of Atlantis, the elaborate miniature work of ancient Greek and Roman-style buildings, landscapes, temples, the volcano, the destruction of Atlantis, and the giant crystal ray weapon, were the work of the special effects production company Project Unlimited, supervised by Gene Warren, Wah Chang, and Jim Danforth, along with the MGM production staff supervised by A. Arnold Gillespie. They coordinated their work with George Pal, who worked closely with the production designer and art director George W. Davis and William Ferrari.
The film's prologue, describing the legend of Atlantis, features stop motion animation, used by producer George Pal earlier in his career for the innovative Puppetoons series.
Voice actor Paul Frees provides the opening and closing narration and is also heard as the dubbed voice of the hero's father, as well as the ruler of Atlantis.
The film generally received poor reviews and was described by film critic Leonard Maltin in his 2002 Movie & Video Guide as "Pal's worst film", saying that it had "poor effects" and that it was: "Occasionally funny – but not on purpose". Author David Wingrove also had similar criticisms in his science fiction film source book: "No expense was spared in buying up footage from Quo Vadis to give it true period flavour. Avoid".
At a preview screening for the film, questionnaires were handed out to the audience asking what scene was their favorite. One person, apparently recognizing the footage taken from Quo Vadis, wrote, "The scene where Robert Taylor saved Deborah Kerr from the fire".Dell Four Color #1188 (May 1961)