Blautopf Blaubeuren

The Blautopf (German for Bowl of the Blau, "blau" means blue) is a spring that serves as the source of the river Blau in the karst landscape on the Swabian Alb's southern edge, in Southern Germany. It is located in the city of Blaubeuren, approximately 16 km (10 miles) west of Ulm. It forms the drain for the Blau cave system and feeds the river Blau, which after 14.5 km (9 miles), flows into the river Danube in the city of Ulm. Because of its high water pressure, the spring has developed a funnel-like shape, which at its deepest point has a depth of 21 metres (69 ft). The water's blue colour is the result of chemical properties of limestone densely distributed in the water.

http://en.wikipedia.org/wiki/Blautopf

Blautopf Blaubeuren

The Blautopf (German for Bowl of the Blau, "blau" means blue) is a spring that serves as the source of the river Blau in the karst landscape on the Swabian Alb's southern edge, in Southern Germany. It is located in the city of Blaubeuren, approximately 16 km (10 miles) west of Ulm. It forms the drain for the Blau cave system and feeds the river Blau, which after 14.5 km (9 miles), flows into the river Danube in the city of Ulm. Because of its high water pressure, the spring has developed a funnel-like shape, which at its deepest point has a depth of 21 metres (69 ft). The water's blue colour is the result of chemical properties of limestone densely distributed in the water.

http://en.wikipedia.org/wiki/Blautopf