Begin in St. Stephen’s Cathedral, right in the heart of Passau’s Altstadt. Its pale baroque interior is wonderfully theatrical, and the organ—one of the world’s largest cathedral organs—is the main attraction. Allow about an hour; on Saturdays, services or rehearsals can affect access, so check the cathedral’s noticeboard when you arrive. Entry is generally free, though organ concerts cost extra, often around €10–20. From here, everything in the old town is comfortably walkable.
Follow your Old Town walking tour through the narrow lanes around Steinweg, Residenzplatz, and the riverside streets, pausing at viewpoints toward the meeting point of the Danube, Inn, and Ilz. This is best enjoyed without rushing: look up at the colorful façades and wander down toward the Danube promenade for a different perspective on the city. After roughly 1½ hours, stop at Café Blum in the Old Town for a slice of traditional cake, coffee, or a light lunch. Budget approximately €8–15 per person; it is a popular central stop, so expect a short wait at peak afternoon times.
Make your way to Veste Oberhaus for the broadest views over Passau. From the Altstadt, walk across the Luitpoldbrücke and take the city bus or the seasonal fortress access option up Oberhaus hill; walking is possible but steep and takes around 25–35 minutes. Allow two hours for the ramparts, viewpoints, and fortress museum, checking the day’s closing time before setting out—summer hours are commonly until early evening, with museum admission usually around €6–8. Return to town and finish at Wirtshaus 4 im Stadtpark, a relaxed beer-garden-style setting for Bavarian dishes and local beer. Reserve or arrive early on Saturday evening; plan on €20–35 per person, and allow about 1½ hours.