A considerable number of cycling paths in Europe follow along rivers; they are often the classic towpaths that run on the bank that have been re-adapted for the bicycle, and at other times local roads with low traffic; cycling paths running along a river generally do not present great difficulty in grade changes and therefore are suitable for “Sunday cyclists”; these factors have contributed to their popularity.
The most famous, and probably the longest, bike path along a river is the Donauradweg which runs from the source of the Danube in Donaueschingen all the way to Budapest. The stretch that is best equipped is the Austrian section between Passau and Vienna.