Text in English & German. The beautiful Lau, the heroine of Eduard Mrike's story, is only half a water spirit -- her mother was a human woman, and her father was a water nix of royal blood. She has thin webs between her toes, but apart from this she is not externally different to a human being. Because she cannot laugh and can bear only dead children, her husband, the Donaunix, sends her to the Blautopf lake. Before she can be permitted to return, she must laugh five times. The Blautopf is located in Blaubeuren, and is the source of the river Blau. It is a "pot spring", and connected to a cave system that was first studied in the 1950s. One of the great caverns discovered by explorers -- the so-called "Mrike-Dom" -- is 25 m wide, 30 m high and 125 m long. The spring waters are deep blue in colour, and change from turquoise blue to dark blue as the light shifts -- on overcast days, the water actually appears to be almost black. During Germany's Romantic period, the Blautopf gave rise to all kinds of speculations and stories, and Mrike, one of the most prominent exponents of Swabia's group of Romantic poets, who spent a night in Blaubeuren during a journey in 1840, took his inspiration from this striking place.