Strömsholm Palace, sometimes called Strömsholm Castle, is a Swedish royal palace. The baroque palace is built on the site of a fortress from the 1550s, located on an island in the Kolbäcksån river at the west end of Lake Mälaren. The palace has interiors from the 1700s and an important collection of Swedish paintings. Strömsholm is one of eight royal palaces managed by the National Property Board. The castle is open to the public, mainly in spring and summer, but also some days throughout the year.