From my sister-in-law :)
Dalarna is the most traditional region in Sweden. The area of Lake Siljan is the most traditional area of this unique region of Sweden
Siljan, in Dalarna in central Sweden, is Sweden's sixth largest lake. Siljan reaches a maximum depth of 120 m (390 ft), and its surface is situated 161 m (528 ft) above sea level. The largest town on its shore is Mora.
The lake is located around the southwestern perimeter of the Siljan Ring (Swedish: Siljansringen), a circular geological formation which was formed 377 million years ago in the Devonian by a major meteorite impact. The original crater, now mostly eroded, is estimated to have been about 52 km (32 mi) in diameter and is the largest known impact crater in Europe (excluding Russia).