Blautopf, 89143 Blaubeuren, Germany
Literally translated to "Blue pot", it is a spring that serves as the source of the river Blau. It is a drain for the Blau cave system, originating from a funnel-like shape with a depth of 21 metres (69 ft). The water's peculiarly blue color, varying in intensity depending on weather and flow, is the result of physical properties of the nanoscale limestone particles densely distributed in the water.
Location of Blautopf