Kastelholm Castle is a Swedish-built medieval castle located off Road 2 in Sund, Åland, Finland, approximately 25 kilometres (16 mi) northeast of Mariehamn, overlooking a fjord to the south of the village of Kastelholm. Along with Hämeenlinna, Olavinlinna in Savonlinna, Raseborg, and Turku, Kastelholm is one of only five surviving Finnish medieval fortresses that are also considered to be architecturally substantial. Built in the 14th century, and held in fief during the Middle Ages by various nobles, feudal chiefs, and kings, it had significant period in the 15th and 16th centuries.