Twenty Thousand Leagues Under the Seas · Jules Verne, 1870
How far is twenty thousand leagues?
~80,000km
About 80,000 km, roughly twice round the Earth. It's how far they travel, not how deep they go.
From the bookReal world
A common mix-up: the title isn't a depth. Twenty thousand leagues is the distance the Nautilus covers in under ten months, from the seas off Japan, across the Pacific and Indian Oceans, through the Mediterranean, down to the South Pole and up to the Maelstrom off Norway.
At about 4 km to the league, that's around 80,000 km. The route on this map takes the short way between the stops Verne names, so it's a sketch of the voyage and comes out shorter than the title.
Follow the whole voyage