The Donau, also known as the Danube, is the second-longest river in Europe, stretching about 2,860 kilometers. It flows through ten countries, including Germany, Austria, and Hungary, before emptying into the Black Sea. The river is an important waterway for trade and transportation, connecting various regions and cultures. The Donau is famous for its scenic beauty and historical significance. It passes through several major cities, such as Vienna and Budapest, and is lined with picturesque landscapes, vineyards, and castles. The river also supports diverse ecosystems, making it a vital habitat for many species of fish and birds.