Between Passau and Neuberg on the Inn river lies a small and wonderful klettergarten. In 1971 a mountain guide by the name Manfred Zimmerman explored climbing in the area in anticipation for operating a climbing school. He thereby bagged many of the first ascents and opened the stone schoolroom to the public climbing community. The area has a diversity of climbing options with grades from 5.1-5.12a The routes are mostly short and there are many boulder problems. Emanuel Hofer has compiled a nice and informative website about the area: www.inntalklettergarten.de/index.html If you understand Deutsch, the above website should cover all topos and info you need.
From Passau, take the B12/Neuburger strasse toward Neuburg am Inn. When you get to Neuburg, find the castle, and turn toward the river Inn (you will be passing the castle on your right). Park at the river and take the bike path upstream until the crags appear.