Die schwarze Donau - Ein Fluss verschwindet (2010)

For millions of years, the Danube has flowed east from the Black Forest to the Black Sea. At the upper reaches of the river, only a valley bears witness to the fact that a mighty river once paved its way here. From here, part of the water flows into Lake Constance, joins the Rhine and makes its way to the North Sea. Filmmaker Axel Nixdorf accompanies speleologists who take a closer look at the extraordinary phenomenon of the disappearing underground river. Driven by the idea of discovering what is probably Germany's largest cave system in the mountain, they have been working towards the Danube for over 20 years. Dives in the spring of the Aach end after only 600 meters due to collapsed cave ceilings.