Roll out of Pettendorf and follow the Regen river before the first castle ruin at Donaustauf appears. Three more castles follow — Gebelkofen, Abbach and Etterzhausen — with the Donau and two nature reserves, the Mattinger Hänge and the Greifenberg und Waltenhofener Hänge, in between. The 75.7 km loop is 99% paved, with one small unpaved stretch, and 654 m of climbing along the way. Then it's back to Pettendorf.