Perhaps the most famous of all Verne's works, 20,000 Leagues Under the Sea (or, in a slightly stricter translation, 20,000 Leagues Under the Seas) was first serialized in 1869 and 1870. The Nautilus was likely inspired by the Plongeur, the first mechanical submarine, which had first been tested in 1863, and had appeared in the Exposition Universelle in 1867, where Verne is known to have been. The name itself is a tribute to one of the earliest sucessful submarines, Robert Fulton's Nautilus, which had been built in 1800. The 20,000 leagues is about 80,000 kilometers.
I'll be reading Lewis Mercier's translation, from 1873. It is notorious for not being great as a translation, but it happens to be the hardcopy I have on hand. I have another, more modern translation, somewhere, but for some reason I cannot find it. I will, however, be comparing with F. P. Walter's well regarded modern public domain translation from the original French.
Favorite Story and Family Theater both did adaptations of the tale to radio, so I will try to fit those in if I can.
