The trio build a raft and set sail for a port they named after Axel's fiancée, Port Grauben. Five days into their sail, they witness a battle between an Ichthyosaurus and Plesiosaurus. The Ichthyosaurus wins, and the travellers are hit with a four-day storm and take shelter by some overhanging rocks. The storm had caused them to travel only some miles north of Port Grauben, so they set on land to track Saknussem's original route once more. They cross a plain of bones and into a forest inhabited by giant Mastodons led by a 12-ft high Proteus, a mythological human. Stunned, the three flee the forest for the Lidinbrook Sea and enter a dark tunnel that plunged deep into rock which they blast through with dynamite. The explosion causes an earthquake, and they become trapped in an active volcano shaft which projects them to the surface of the Earth by Mount Etna in Sicily.