The Danube Cycle Path
This classic among long-distance cycle paths was completed in around 1980 by expanding and adding asphalt to old towpaths running alongside the river. Tourism associations from the Austrian states of Upper and Lower Austria and Vienna introduced consistent signposting, hotels and restaurants started settling by the river and maps and travel guides were published. Today, the Danube Cycle Path is continuously flat and extremely well-kept, both adults and kids will be able to enjoy the route between Passau and Vienna without any problems.
Both expansion and maintenance of the Danube Cycle Path is continuously taken care of and now one has the option of cycling either on the north or south shore at most points along the cycle path. You can cross over the river on bridges, walkable water-power generators or ferries, most of which you can hail (see table bike distances for further information).
You should earmark about 1 week to cover the total 320 kilometres (198 miles) - there is a lot to discover along the way. If you, like most people, choose to cycle from west to east, your final destination will be the metropolis of Vienna, where you can holiday for a further week without any problems.
For more information on the flooding problems along the Danube Cycle Path see here.