The Blautopf in Blaubeuren is connected to the Danube via the Blau River. In this water system, there is a population of mermaids and water spirits. The mermaid Lau, married to a prince from the Black Sea, is beautiful but melancholic. She cannot have children—unless she laughs five times. How can a melancholic mermaid be made to laugh five times? It is only conceivable if she visits the human world, where there are amusing situations. Through a well in the Blaubeuren inn, Lau emerges. The innkeeper befriends the visitor, provides her with suitable clothing, and dries her feet (after all, she has feet, not a fish-like lower body). Drying her feet tickles Lau—she has to laugh! And now, the four other occasions for laughter are sought and found—entirely harmless reasons.