Blautopf

The Blautopf is the outlet of a large karst system draining the Swabian Jura, a funnel-shaped pool about twenty-one metres deep whose water appears deep blue; the colour comes from very fine limestone particles scattering light rather than from any dye or mineral tint, and it shifts with light and flow. Cave divers have explored the flooded system behind it since the 1950s, mapping more than fifteen kilometres of passages including large air-filled chambers reached only by diving through sumps. Eduard Mörike set his story of the Beautiful Lau, a water sprite living in the pool, here. A restored hammer mill stands beside it.

What you actually see

• The blue pool - colour produced by fine limestone particles in the water.
• The cave system - over fifteen kilometres mapped by divers behind it.
• The hammer mill - a restored forge beside the spring.
• The Mörike legend - the water sprite story attached to the pool.

When to go

April to October; the colour is strongest in bright light and clear conditions, and heavy rain turns the water cloudy and brown for days. Diving is not open to visitors.

Honest expectations

After rain the pool loses its colour entirely for a time. The site is small, seen in half an hour. The cave system is closed to all but research divers.

Nearby

Ulm lies east; the Jura caves of the Lone valley are north.