Lake Hallwil lies in the Seetal valley on the border between the cantons of Aargau and Lucerne and, at around 10 kilometres in length, is one of the largest natural lakes in the Swiss Plateau. It is known for its clear water and extensive reed beds, which provide habitat for numerous water birds.

The most significant monument on the lake is Hallwyl Castle, a two-part medieval moated castle standing on islands in the Aabach. It is one of the best-preserved moated castles in Switzerland and is open to visitors from April to October. A circular walking trail of around 28 kilometres leads around the entire lake; shorter sections are also possible. In summer, passenger boats operate on the lake.

Lake Hallwil is reachable by S-Bahn (line S41) from Zurich or Lucerne via Lenzburg or Seon. By car, cantonal roads run through the Seetal valley; parking is available in most lakeside villages.