The Danube is the second-longest river in Europe, flowing through ten countries, including Germany, Austria, and Hungary. It stretches approximately 2,860 kilometers (1,780 miles) from its source in the Black Forest to its delta at the Black Sea. The river is an important waterway for trade and transportation. The Danube is known for its diverse ecosystems and rich cultural history. It passes through several major cities, such as Vienna and Budapest, and is home to numerous historical sites. The river also supports various recreational activities, including boating and fishing, making it a vital resource for the regions it traverses.