Aronnax tells him about Nemo's "bank"—the treasure at the bottom of the ocean—and tries to convince him that maybe leaving isn't the best idea.
Ned doesn't listen. He's already planning for next time.
Soon, it becomes clear they're moving away from the coast. Ned skulks out. No escaping now. Aronnax is relieved. Now he's got more time to work.
Later that night, Nemo shows up and asks Aronnax if he wants to go for a nighttime jaunt.
Nemo and Aronnax suit up, and soon they're walking on the ocean floor.
During their walk, Aronnax spies a strange red glow off in the distance. He thinks that maybe Nemo's taking him to some kind of underwater city, a city filled with exiles like him.
They keep heading toward the light, up the slope of a mountain. Nemo keeps climbing without rest, and Aronnax can do nothing but follow.
After two hours of walking, our two dudes get near the top of the mountain, where they encounter some freaky crustaceans. Nemo's unfazed. They keep walking.
They reach a plateau. Off in the distance, Aronnax can see some piles of stones that look… unnatural. They look like the work of man.
Nemo waves Aronnax onward. Finally, they reach the summit.
Down below, Aronnax can see the crater of a volcano, spewing lava. Beyond that, he can see what looks like a city, an ancient city, built in the style of the Greeks or Romans. It has been destroyed, and it is crumbling.
Nemo picks up a piece of chalky stone and writes this on a rock: "ATLANTIS."
Say what? They're visiting Atlantis, the lost city, a mythical place that's apparently not so mythical at all.
Aronnax is bummed out that they don't have much time to explore the place.
They leave after an hour and head back to the Nautilus. As is the case with most vacations, the trip home seems to take forever.