The Ilztalbahn begins at platform 1a, the so-called Waidlergleis, in Passau Hauptbahnhof. From there it runs to the west over the present-day timetable route (Kursbuchstrecke or KBS) 880, branches off about 2 kilometres to the north and crosses the river Danube on the Kachlet bridge not far from Kachlet power station. Thereafter it climbs into the Bavarian Forest and reaches the valley of the river Ilz behind Tiefenbach. It then follows the Ilz northwards. In the two Fürsteneck Tunnels the line leaves the Ilz valley and heads east into the Osterbach valley as far as Waldkirchen. From here it turns north again towards Freyung. In Waldkirchen the 26.9 km long route to Haidmühle via Jandelsbrunn branches off.