On the banks of Danube River, the second longest river in Europe

 "The Blue Danube" is the common English title of "An der schönen, blauen Donau," a waltz by the Austrian composer Johann Strauss II, composed in 1866. Originally performed on 15 February 1867 at a concert of the Wiener Männergesang-Verein, it has been one of the most consistently popular pieces of music in the classical repertoire. 

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(on the second longest river in Europe) For hundreds of years the Danube River has been an important route for trade and travel throughout central and southeastern Europe. The castles and fortresses along the river’s banks once protected great empires. Some of them still draw tourists to the area. The Danube starts in the mountains of western Germany and flows for some 1,770 miles (2,850 kilometers) to the Black Sea. Along the way, it passes through nine countries. A major trade route, countries along the river ship goods from such ports as Belgrade, Serbia; Budapest, Hungary; Vienna, Austria; and Regensburg, Germany.
+ Sailors from ancient Greece began exploring the Danube as early as the 600s BCE. The river later served as the northern boundary of the Roman Empire. Several other empires took control of the lands along the river over the years. Eventually people began to use it for trade. They then began to discuss who would be allowed to use the water for travel or any other purpose. (An agreement in the mid-1800s opened the Danube to the shipping of the nations traversed by the river.)

+ The Danube played a vital role in the settlement and political evolution of central and southeastern Europe. The river’s majesty has long been celebrated in music. The famous waltz An der schönen, blauen Donau (The Blue Danube), by Johann Strauss the Younger, became the symbol of imperial Vienna. In the 21st century the river has continued its role as an important trade artery. It has been harnessed for hydroelectric power, particularly along the upper courses, and the cities along its banks -- including the national capitals of Vienna, Budapest, and Belgrade -- have depended upon it for their economic growth.

+ The sparsely populated eastern reaches of Bavaria may be somewhat overshadowed by this German federal state's more popular tourist attractions, but they preserve historical treasures that rival those of their neighbors. Top billing goes to Regensburg (featured here), one of Germany’s prettiest and liveliest cities. The capital of the Oberpfalz region of Bavaria, Regensburg dates back to Roman times and was the first capital of Bavaria. Two thousand years of history bequeathed the city some of the region’s finest architectural heritage, a fact recognized by UNESCO in 2006. Though big on the historical scale, today’s Regensburg is a laid-back, unpretentious sort of place -- and its tangle of old streets is quite a joy to explore. (From here the Danube gently winds its way to the Italianate city of Passau [near the Austrian border], where the Danube is joined by the Inn and Ilz rivers.)