Soon you pass Steyregg and its splendid 11th/12th c castle, but the latter only opens its gates for events taking place there.
Now you leave the Danube for a while and head toward Mauthausen. It was founded by the Babenbergs as a place to exact tolls (“Mautstätte”, hence the name “Mauthausen”, literally “toll house”). It gained notoriety as the site of the biggest Austrian Nazi concentration camp (now a memorial site).
At Castle Pragstein you can learn everything you ever wanted to know about making pills and mixing ointments, as it is home to Austria's only pharmacy museum.
At Au an der Donau or at the latest at Mitterkirchen im Machland you can take a side trip to Perg, the district seat for an enjoyable break. Alternatively you could combine your next stop with a visit to the Celtic village in Mitterkirchen, an open-air museum. It helps you vividly understand daily life in 700 B.C. Not far from there you can also visit Baumgartenberg Abbey. The abbey church is considered a gem of the Baroque era due to its magnificent stuccowork. From here the river guides you at a leisurely pace to Grein, the “Pearl of the Strudengau.”