This circular tour owes its name to several fascinating geological phenomena: a river that flows into two seas, an underground cave system, a unique spring, and the volcanism of the Hegau region. In Immendingen and Möhringen, a large portion of the Danube's water simply disappears into sinkholes. What flows above ground eventually empties into the Black Sea. But what vanishes and flows underground reappears two to three days later at the Aach spring in the Hegau. From there, the Danube flows into Lake Constance and then, via the Rhine, into the North Sea. Even the view of the volcanoes from the highest point of the bike tour is impressive. The individual volcanoes rise from the landscape like cones. But the Höwenegg volcano is even more surprising up close. You stand in awe before the shimmering green "crater lake"—which isn't actually a crater, but rather a result of basalt mining. This nature reserve is also one of the most important sites where the prehistoric horse, which was native to this area millions of years ago, was discovered.
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Tourist Information Danube Uplands
