Twenty Thousand Leagues Under the Seas, published in 1870, is a science fiction novel by Jules Verne that follows the adventures of Professor Pierre Aronnax, his servant Conseil, and Canadian whaler Ned Land as they embark on a journey aboard the submarine Nautilus, commanded by the enigmatic Captain Nemo. The novel is known for its imaginative depiction of undersea exploration and the scientific wonders of the ocean.

The story begins in the 1860s when reports of a mysterious sea creature terrorizing ships in the oceans prompt various expeditions to uncover the truth. Professor Aronnax, a marine biologist, is invited to join a U.S. Navy expedition led by Captain Nemo aboard the frigate Abraham Lincoln. Shortly after departing, the crew encounters the creature, which turns out to be the Nautilus, a powerful submarine.

The Nautilus, captained by the reclusive and enigmatic Captain Nemo, captures Aronnax, Conseil, and Ned Land, who becomes a reluctant member of the crew. The trio soon finds themselves immersed in a series of extraordinary underwater adventures. They travel across the world's oceans, witnessing breathtaking marine life, underwater landscapes, and historical shipwrecks.

During their journey, they encounter various challenges, including battles with giant squid, shipwrecks, and encounters with hostile underwater creatures. The crew also visits incredible locations such as the lost city of Atlantis, the Arctic Ocean, and a variety of coral reefs.

As they explore, Captain Nemo reveals his disdain for the surface world and the injustices he perceives in society, explaining his choice to live beneath the waves. While Aronnax is fascinated by Nemo's scientific knowledge and the wonders of the ocean, Ned Land becomes increasingly frustrated with their captivity and yearns to return to land.

The story reaches a climax when the Nautilus is caught in a violent underwater whirlpool, which ultimately leads to its destruction. Aronnax, Conseil, and Land manage to escape the submarine just in time. They find themselves washed ashore, and Aronnax reflects on the extraordinary journey they've had.