Suomenlinna is a sea fortress built from 1748 onwards on islands at the entrance to Helsinki harbour, spanning 210 hectares across six islands with 200 buildings and 6 km of defensive walls. Originally constructed by Sweden using bastion fortification principles, it served three sovereign states before becoming Finland's most popular tourist attraction and residential district with 850 inhabitants. Visitors explore the well-preserved Swedish and Russian period fortifications, utilitarian buildings, and landscape that exemplify 17th-18th century military architecture.
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