Aachtopf

In 1719, the assumption that the spring water came from the sinking of the Danube was first expressed in a publication by F. W. Breuninger. However, proof was only achieved on October 9, 1877, when the geologist Adolf Knop from the Karlsruhe University of Technology added 10 kg of sodium fluorescein, 20 t of salt and 1200 kg of shale oil to the water in the Danube sinkhole. After 60 hours, all three substances could be detected in the spring pot, which was reflected in the magnificent green glow of salt water with a distinct creosote-like taste.
In 1886 there was the first attempt at diving to a depth of 12 m (one of the first cave diving attempts in the world), where the difficult-to-surmount nozzle is located, a narrow area in which the water has a strong current.
The spring cave was researched by Jochen Hasenmayer from the 1960s. A hall with sinter basins and stalactite remains was discovered, which shows that this hall was once an air-filled stream cave. In the years from 1980 onwards, the Aachhöhle was intensively researched by Harald Schetter. The Aachhöhle has been re-measured by Jürgen Bohnert, Frank Liedtke, Stephan Liedtke and Tobias Schmidt since 2001. After 500 m north, the cave ends in a massive collapse, which can also be seen on the surface as a large sinkhole in the forest. After 14 years of excavation, the continuation of the Aachhöhle was discovered on the northern edge of the sinkhole. Since the chemical composition of the water here does not match that of the Aachhöhle, it is assumed that it must be one of several tributaries. Therefore the cave from here on is called the Danube Cave.
In April 2017, the first discovery of a cave fish in Europe was announced. It is a largely pigmentless and probably blind population of the stream loach (Barbatula barbatula). It was discovered in the branched cave system of the Aachtopf, but probably occurs in the entire 250 square kilometer cave system up to the sinking of the Danube

Great photo opportunities were almost all alone
in the afternoon endless people

The Aachtopf is the largest spring in Germany. From the small bridge you can see very well how the water bubbles out of the ground. Most of the water comes from the Danube and seeped in the area of Immendingen.