Lago Calafquén straddles the border between the La Araucanía Region and Los Ríos Region in southern Chile, forming part of the drainage basin of the Valdivia River. It is one of the Seven Lakes of the Los Ríos circuit, a scenic route that also includes Pullinque, Panguipulli, Neltume, Pirihueico, Pellaifa, and Riñihue. The lake is glacial in origin, dammed by moraine, and sits at coordinates 39°31′S, 72°09′W. It stretches approximately 25 kilometers in length and 7.7 kilometers at its widest point, covering a surface area of 114.9 square kilometers with a shoreline of roughly 122 kilometers. The average depth is 115 meters, reaching a maximum of 212 meters, making it a substantial and deep body of water. The Villarrica Volcano lies to the north of the lake and is visible from the surrounding area.

The primary inflow is the Llancahue River, and the lake drains via the Pullinque River. The name derives from Mapudungun and is variously translated as "lake like a sea" or "another lake," reflecting its considerable size.

The towns of Lican Ray, Coñaripe, and Calafquén are situated on the lake's shores. Coñaripe features a beach nearly 3 kilometers long, described as one of the longest in the Los Ríos Region, and offers cabins and services that support water-based activities including yachting and sport fishing. The lake is noted for relatively warm waters compared to other lakes in the region, which makes it a popular destination for water sports. The surrounding landscape includes Valdivian rainforest and proximity to the Mocho-Choshuenco volcano, and the area carries living Mapuche cultural heritage, with local crafts and Chilean-Mapuche fusion cuisine available in the lakeside towns.