The Veste Oberhaus is a large fortified complex on the wooded hill directly above Passau's old town, connected to it by a steep footpath (about 20 minutes up) or by a seasonal shuttle bus from the town centre. Built by the powerful prince bishops of Passau in the 13th century, it served as their stronghold and residence for over 500 years.
Today it houses the Passau City Museum, which covers the city's history from Roman times through the episcopal era to the present. The collection is substantial and well-presented. But the main draw is the view from the citadel walls: the confluence of the Danube, Inn, and Ilz rivers is visible below in one panoramic sweep, each river running a different colour — the blue-green Danube, the darker Inn, and the small black Ilz. It is the definitive view of Passau and worth the climb for that alone.