They eventually encounter a subterranean ocean, which they name the Saknussem Ocean, and make a raft from the stems of giant mushrooms to cross it. Somewhere in the middle of the ocean, they pass through the center of the earth and their raft begins circling in a mid-ocean whirlpool. The professor deduces that must be the center of the earth, because the magnetic forces from north and south meeting there are strong enough to snatch away even gold in the form of wedding rings and tooth fillings. They somehow manage to cross the ocean, and, completely exhausted, reach the shore on the other side.
Despite the dangers of their journey, no one has died, but that soon changes. Gertrude, the duck, loses her life to Saknussem, who can’t control his hunger and eats her. Soon after a mild earthquake occurs; Saknussem is buried under a shower of heavy stones, but right behind the collapse the rest of the group comes upon the sunken city of Atlantis. They are now faced with one ominous question: How will they return to the surface?