The submarine was not known by any person in the world except for the one and only great Captain Nemo. "For you I should merely be Captain Nemo, and you and your companions will be for me merely passengers on the Nautilus"(pg.71-72).
The men are then well fed and clothed, and for months live on this sub. They only eat fish and fresh things from the sea, and the clothes were all made of some material from the sea. they enjoy the ship but are sometimes homesick, in a way that they miss real meat, and want to walk on dry land. But Captain Nemo doesn't allow that because he assumes the men would go back and tell the people of the great Nautilus.
Soon the men forget what they really had even started their sea adventure for in the first place. But one night they realized what they had really come to look for. The Nautilus had brushed up on a cave and some seaweed when Monsieur reminds himself that those are the types of caves giant squids live in. Conseil now also remembers that fact and then says something that is the turning point: "I myself can remember having seen a large boat being dragged down by the arms of a squid"(pg.333).
Conseil tells the legend of how the painting in the church got there, how a crew of men attempted to capture the monster by shooting it, but it did not work. Them they finally got an idea that they thought would work. The men tried to haul the monster up but it was too heavy; the net broke and the giant squid dove back down to the ocean depths(without a tail because it had torn off when trying to escape.) The men were very fascinated by the story. They all thought for a minute and then it hit them. The monster that was roaming the waters was a giant squid that could drag down a boat by its arms. The crew figured that the beast was a whopping thirty feet.
At the end the Nautilus had traveled 20,000 leagues(almost 60,000 miles) in the water. Unfortunately the men never did catch the monster. The legend of the great beast is still around for people to hear and read, but in 20,000 Leagues Under the Sea Jules Verne tells the story like he were Captain Nemo of the Nautilus.