Danube Bike Trail: Part 1Fra Donaueschingen to Passau. From its headwaters in the Black Forest of southwestern Germany, the Danube flows through some of the most beautiful landscapes in Europe. Pristine flood plains, picturesque villages and small towns, and a wealth of cultural landmarks line the river as it begins its long march to the distant Black Sea. These tranquil valleys are also ideal for cycling. In recent years, many of the paths and lanes along the river have been