Willy Fog and Hans start off down another passage in search of water. The rest of the group wait for them to return. Finally Rigodon and Tico start out to look for them as they are taking such a long time. Willy Fog and Hans find an underground river. They have to perforate the wall with their pickaxes. When they finally achieve this, a stream of boiling water spurts our but the water quickly cools. They are very relieved and start back. The professor takes notes in his notebook and they all continue the journey lit by their torches and accompanied by the unexpected river.