https://www.inyourpocket.com/helsinki/suomenlinna-sea-fortress_165736v
Holding some of Finland’s most important military history, Suomenlinna Sea Fortress is a UNESCO World Heritage Site and one of Helsinki’s top tourist...
sea fortresssuomenlinnasightseeinghelsinki
https://suomenlinna.fi/en/explore/history/
Situated on a group of islands off Helsinki, Suomenlinna was built during the Swedish era as a maritime fortress and a base for the Archipelago Fleet.
the fortressofficial websitehistorysuomenlinna