Boat trip on the Danube to Walhalla, the German Hall of Fame built in the mid 19th century. The place is really impressive both inside and out. The hall contains busts of German speaking luminaries including more recent people like a bust of Einstein (which Rowan liked in particular) and Sophie Scholl.
Back in Regensburg we went for a really nice walk through the old town. A real shame the bridge from 1130 was being renovated.