Munkholmen Island was Trondheim’s execution site in the Viking era. Benedictine monks built a monastery on the island in the early 11th century, probably one of the earliest monasteries in Scandinavia. In 1658 it was converted into a prison and fortress, and later a customs house. Its most famous inmate was the Danish Count Peder Griffenfeld, who spent 18 years as a prisoner there. Today “The Monks' Island” is a popular recreational area, with a nice beach and a restaurant, which is open in the summer months from May to September.