The Danube between Passau and Linz is one of the loveliest stretches of the whole river, and near Oberranna, on the Upper Austrian bank, it flows quietly between steep wooded slopes, dark and almost gorge-like. Here, beside the water, archaeologists found a small Roman fort, a Kleinkastell, part of the Danube Limes that guarded the northern frontier of the province of Noricum. Its remains are now protected under a modern shelter, and it forms part of the UNESCO listing of the Frontiers of the Roman Empire along the Danube.
The fort was small, holding perhaps a few dozen soldiers to watch the river and the road along it, and its walls and towers have been preserved to a surprising height, giving a real sense of its layout. A short distance downstream is the abbey of Engelszell, the only Trappist monastery in Austria, where the monks brew beer and make liqueurs, and further along, the river makes its famous loop at Schlögen, a tight bend where the water reverses direction around a forested spur. A viewpoint above the loop is one of the classic sights of the upper Danube.
Riding along the Danube here is relaxed and beautiful. The road on the southern bank follows the river closely, with gentle curves, views across the water and small villages with inns and moorings for river cruise boats. Side roads climb away from the river into the Innviertel and the Sauwald hills, with sharper bends, farm traffic and wide views. Ferries cross the river at several points, linking the two banks and making for interesting loops. Be aware of cyclists, especially in summer, as the Danube cycle path is one of the most popular in Europe.
The nearest towns are small, with limited services, but Engelhartszell and other villages along the river have fuel stations or are close to them, and Passau, a little upstream, has everything you need. Riverside inns serve local fish such as pike-perch, as well as Austrian classics like schnitzel and roast pork. Remember that Austrian motorways require a vignette, though you will hardly need them here.