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Stream the full National Geographic City Under the Sea movie online for free in crystal-clear HD quality. No downloads required—just press play and enjoy the action, complete with English subtitles for an enhanced viewing experience.

With a host of problems threatening the earth's surface, is underwater living a viable alternative? Meet the scientists who believe that permanently submerged colonies are not just possible, but imminent. National Geographic follows the scientists as they tackle the hypothetical challenge of housing 100 families below the ocean's surface and race to overcome obstacles such as bone-crushing pressures, ravaging storms and scalding volcanic fluids to create self-sufficient underwater communities