Twenty Thousand Leagues Under the Sea also known under its longer title, Twenty Thousand Leagues Under the Seas: An Underwater Tour of the World, is classic science fiction novel written by Jules Verne that was first published in 1870.
In the story, Captain Nemo pilots his vessel, the Nautilus, on an adventure in search of a sea monster that was sighted by a number of ships in 1866. The American government sponsors the mission. This great adventure story is notable for being more scientifically accurate than some of Verne's other novels. In particular, the description of the Nautilus is rather prophetic and a fitting description for modern submarines. While there were submarines in existence when the book was written, they were primitive affairs and it took a feat of imagination for the writer to produce his vision of what an underwater craft would look like in the future.
Readers should note that "Twenty Thousand Leagues" is not the depth to which the Nautilus dives -- the ocean is not that deep -- but describes the distance traveled under the surface of the ocean as the ship and crew adventure around the globe.