The Black Sea.
The Danube River is the second longest river in Europe, after the Volga. It originates in the Black Forest region of Germany and flows through ten countries, including Austria, Hungary, Serbia, and Romania, before emptying into the Black Sea. The Danube is an important transportation route and is also a major source of hydroelectric power. The river is about 2,850 km long and passes through a variety of landscapes, from the rolling hills of Bavaria to the vast wetlands of the Danube Delta.