The "Wimsener Höhle" situated in the "Swabian Highlands" is the only German cave which can be visited by a boat. The boat brings the visitors about 70 m into the rock. Into the cave there are versatile colored rocks and the water is very cold and clear. The second name of the cave "Friedrichshöhle" depends on the fact, that the cave was first visited by the the King "Friedrich of Württemberg" in the year 1803.
Going with the boat into the cave you have to aspirate your head for not activating at the rocks.
The landscapes around the cave are also very nice.