Mondsee, Lake in the Salzkammergut, Upper Austria, Austria

Mondsee is a lake in the Upper Austrian Salzkammergut, stretching 9.6 km from northwest to southeast and up to 3 km wide, with a surface of about 14.32 km² and a mean depth of 37 m. Its southwestern shore marks the border with Salzburg. The Drachenwand, a roughly 700 m high cliff, rises above the southern shore, while gentler Flysch hills border the north.

In 1872, remains of Neolithic pile dwellings and numerous everyday objects were found in the lake; the English source dates the discovery to 1864. The site gave its name to the Mondsee culture and has been part of the UNESCO World Heritage "Prehistoric Pile Dwellings around the Alps" since 2011.

The lake gives its name to the Mondsee culture, a Neolithic group identified from pile-dwelling remains found in 1872; the site has been part of the UNESCO World Heritage "Prehistoric Pile Dwellings around the Alps" since 2011. Ian Fleming's 1961 novel Thunderball has Blofeld claim Himmler's jewels were recovered from the lake, and Arno Geiger's 2018 novel Beneath Drachenwand Mountain is set mainly here.

Most of the 25.7 km shoreline is privately owned and not open to the public, so bathers and sailors reach the water at the few public access points. The lake surface belongs almost entirely to a single private plot. The Seeache outflow is regulated at the Klauswehr weir, and the water renews about every 1.7 years.

The lake is one of Austria's last privately owned lakes; in August 2008 owner Nicolette Wächter announced it was for sale. Almost the entire water surface belongs to a single property within the municipality of Mondsee, so most shore plots serve only as lake access. Ian Fleming mentions the Mondsee in his 1961 James Bond novel Thunderball, where Blofeld reports that Himmler's jewel hoard was secretly recovered from the lake.