The Aachtopf is Germany's biggest karst spring, south of the western end of the Swabian Jura near the town of Aach. It produces an average of 8,500 litres per second. Most of the water stems from the River Danube where it disappears underground at the Danube Sinkhole, 12 kilometres (7.5 mi) north near Immendingen and about 14 kilometres (8.7 mi) north near Fridingen. The cave system has been explored since the 1960s, but as of 2020 only a small part has been discovered due to a large blockage after a few hundred metres.
Aachtopf historical postcard, 1910
Aachtopf view from spring towards river
Panorama
A karst spring or karstic spring is a spring that is part of a karst hydrological system.
A 130-metre (430 ft) deep karst spring of the Cetina River in Croatia
The Vrelo Bune (English: Wellspring of the Buna) with the Blagaj Tekke under a limestone cliff in Bosnia
Blautopf (Blue Pot), karst spring of the River Blau (River Blue) in Blaubeuren, Swabian Jura
Fontaine-de-Vaucluse, karst spring of the Sorgue, characterised by an upward movement of water from the depth of over 315 metres (1,033 ft)