Sollerön is the largest island in Lake Siljan and a locality situated in Mora Municipality, Dalarna County, Sweden. It had 901 inhabitants in 2010. The island is home to several notable archaeological and historical sites, including Dalarna's largest Viking-era grave fields, a historic church, restored 18th-19th century farmhouses, the Viking museum has now …Sollerön is the largest island in Lake Siljan and a locality situated in Mora Municipality, Dalarna County, Sweden. It had 901 inhabitants in 2010. The island is home to several notable archaeological and historical sites, including Dalarna's largest Viking-era grave fields, a historic church, restored 18th-19th century farmhouses, the Viking museum has now closed.