Schloss Mattsee, Medieval castle in Mattsee, Austria.

Schloss Mattsee stands on a narrow peninsula in the Mattsee that was once cut off from the shore by a deep moat. Of the historic complex, the three-storey south wing with its hipped roof survives, a quarry-stone building plastered and painted white; a few large stone blocks and two sandstone columns recall the former castle. The keep in the north-west corner, the 1558 court tavern (now Gasthof Iglhauser) and the former gatehouse by the moat also remain.

The castle was founded around 1100 by the bishops of Passau and gained prominence in 1398 when it became a summer residence for the archbishops of Salzburg. This connection to Salzburg shaped its development over the following centuries.

The name Mattsee derives from the lake and the estate of the Passau bishops; the castle became the Salzburg archbishops' summer residence, used by Wolf Dietrich von Raitenau and Markus Sittikus for hunting. Today the municipality runs it as a cultural centre for concerts and private events, including the Diabellisommer concert series, and the attic houses the Leonardo Kunstakademie, which teaches various artistic techniques.

Schloss Mattsee stands on a narrow peninsula in the lake, reached by a single entrance; the surrounding walls were still intact in 1837. The south wing keeps three storeys under a hipped roof, with the keep at the north-west corner. The former gatehouse stood by the moat, and the 1558 court tavern now operates as Gasthof Iglhauser.

The ice cellar lies below the castle, not inside it: Obertrum brewer Josef Sigl built it in 1871, and it now serves as a public toilet. The structure is therefore a separate feature of the Schlossberg, reached from the slope beneath the walls.