Suomenlinna

A sea fortress spread across eight islands, six of them fortified, four kilometres out from the centre of Helsinki. The Swedish Crown began building in 1748 against Russia, with Admiral Augustin Ehrensvärd in charge and Vauban’s star-fort principles adapted to bare rock. Its reputation as the Gibraltar of the North did not survive contact: besieged in 1808, it surrendered after two months, and Russia took Finland the year after. It was Sveaborg, the fortress of Sweden, until 1918, when it was renamed Suomenlinna, the fortress of Finland. Most of it passed to civilian administration in 1973.