Kastelholm Castle (Swedish: Kastelholms slott) is a Swedish-built medieval castle located off Road 2 in Sund, Åland, Finland, approximately 25 km (16 mi) northeast of Mariehamn, overlooking a fjord to the south of the village of Kastelholm. Along with Hämeenlinna, Olavinlinna in Savonlinna, Raasepori, and Turku, Kastelholm is one of only five surviving Finnish medieval fortresses that are also considered to be architecturally substantial.