Start at Café Greindl, a convenient choice near Passau’s pedestrian center for a relaxed late breakfast and coffee. Allow about 45 minutes and roughly €10–20 per person. Since it is already close to noon, check today’s service hours before setting off; Saturday tables can fill quickly. After breakfast, wander through the surrounding Altstadt lanes rather than taking a direct route—the compact center is easiest on foot, with most streets around Ludwigstraße and Rindermarkt closed or restricted to traffic.
Make your way to St. Stephan’s Cathedral for around 12:45, allowing 45 minutes to take in the vast baroque interior and the famous organ. Entry to the church is generally free, though concerts or special events may affect access; dress respectfully and keep voices low during services. Afterwards, step straight onto Residenzplatz, one of Passau’s prettiest squares, for a 20-minute pause beside the cathedral. The square is ideal for photos and a breather before the more active part of the afternoon.
From the Altstadt, continue to Veste Oberhaus. The uphill walk takes around 20–30 minutes and is rewarding, but in August it can be hot; the local bus is the easier option if you want to save energy. Allow about 1½ hours for the fortress grounds, museum areas, and panoramic views across the Danube, Inn, and Ilz. Check the fortress’s current Saturday opening hours and admission prices before going; budget approximately €5–10, depending on which areas are open. Later, descend toward the Dreiflüsseeck in Innstadt—on foot, this is a pleasant but longer riverside walk, while a short taxi or local bus ride is practical if the heat is intense. Spend about 45 minutes at the riverfront watching the three waterways meet; the viewpoint is particularly atmospheric in late afternoon, and the nearby promenade makes a good place to linger without adding another fixed stop.