Þingvallavatn is a rift valley lake in southwestern Iceland. With a surface of 84 km² it is the largest natural lake in Iceland. Its greatest depth is at 114 m. At the northern shore of the lake, at Þingvellir (after which the lake is named), the Alþingi, the national parliament, was founded in the year 930.

Þingvallavatn is a rift valley lake in southwestern Iceland. With a surface of 84 km² it is the largest natural lake in Iceland. Its greatest depth is at 114 m. At the northern shore of the lake, at Þingvellir (after which the lake is named), the Alþingi, the national parliament, was founded in the year 930.