Donau is a river located in Central and Eastern Europe. It is the second-longest river in Europe, being 2,888 km long. The river runs through four countries, beginning in Germany and passing through Austria, Slovakia, and Hungary before eventually emptying into the Black Sea. Along the way, the Donau winds its way through beautiful canyons, lush forests, and picturesque cities. Some of these cities include Munich, Vienna, Budapest, and Bratislava. It is well known as a major shipping route used for waterborne transportation and serves as a vital lifeline for industry, tourism, and agriculture.