Ossiacher See is the third-largest lake in the Austrian state of Carinthia, tucked between the forested slopes of the Gerlitzen to the north and the western foothills of the Ossiacher Tauern to the south. It is one of the region's most popular destinations for combining lake life with mountain scenery.

Stretching about 10.2 km from southwest to northeast, and narrowing to just 600 metres between Bodensdorf and Ossiach, the lake offers a striking mix of open water and steep, wooded shorelines. In summer the lakeside towns buzz with visitors, while the surrounding hills make for quiet, scenic walks and cycling routes. In colder months the lake sometimes freezes, drawing skaters, though ice conditions are not officially monitored here.

• Ossiach or Bodensdorf — reachable by local road, lakeside path continues around the shore, easy
• Villach — starting point for the Ossiacherseeradweg R2, roughly 25 km loop around the lake, easy
• Stages 18-20 of the Alpe Adria Trail pass through the lake region, long-distance route, moderate

• Several protected nature and landscape areas surround the lake (including the Tiebel estuary, Jammernspitz and Meerspitz), with restricted access to sensitive habitats
• Walking on the frozen lake may be officially prohibited at times — unlike the nearby Weißensee, there is no dedicated ice warden here
• The rare water caltrop (Trapa natans) grows near the mouth of the Tiebel river

The lake is home to 21 fish species and its reedy shores attract great crested grebes, kingfishers and other notable waterbirds, making it a rewarding spot for nature lovers as well as hikers and cyclists.