The Donauradweg from Passau to Vienna is one of Europe's gentlest long-distance cycle routes, flat enough for a first-timer and scenic enough that experienced tourers still rank it among their favourites.
The route covers roughly 320 kilometres and is almost entirely flat, following the river through the Wachau Valley's terraced vineyards, past Melk Abbey's baroque towers, and into Vienna along a dedicated riverside path. Most riders cover it in five or six easy days, doing 50 to 70 kilometres between stops rather than racing the distance, which leaves afternoons free for a swim in the river or a glass of Grüner Veltliner at a Heuriger wine tavern.
You don't need to be an experienced cyclist for this one — hybrid or touring bikes are available to rent in Passau, and most operators will transfer your luggage between guesthouses each day for a fee, so panniers aren't strictly necessary. The path is well signposted the entire way, and small towns like Dürnstein and Krems arrive often enough that you're never far from a bakery or a bed.
Ride it in May or September rather than peak summer if you can — the vineyards either side of the Wachau stretch are at their most striking then, and the path is quieter. A small practical note: book Melk Abbey's tour slot in advance in high season, since it's the one stop on the route that draws bus tours as well as cyclists.
