is the biggest island in Mälaren
, and covers 91 km². It is located at Stallarholmen
, east of Strängnäs
, and it has about 3,000 permanent residents. It is connected by a bridge to the mainland. It is the largest island in any lake in Sweden.
In the Heimskringla, Granmar, the king of Södermanland, was murdered on this island by Ingjald Illruler.