Danube
Classified as an international waterway, it originates in the town of Donaueschingen, in the Black Forest of Germany, at the confluence of the rivers Brigach and Breg. The Danube then flows southeast for about , passing through four capital cities (Vienna, Bratislava, Budapest and Belgrade) before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.
Danube Sinkhole
The Danube Sinkhole ( or ) is an incipient underground stream capture in the Upper Danube Nature Park. Between Immendingen and Möhringen and also near Fridingen (Tuttlingen), the water of the Danube sinks into the riverbed in various places. The main sinkhole is next to a field named "Brühl" between Immendingen and Möhringen.