Suomenlinna, or Sveaborg, is an inhabited sea fortress composed of eight islands, of which six have been fortified; it is about 4 km southeast of the city center of Helsinki, the capital of Finland. Suomenlinna is popular with tourists and locals, who enjoy it as a picturesque picnic site. Originally named Sveaborg, or Viapori as referred to by Finnish-speaking Finns, it was renamed in Finnish to Suomenlinna in 1918 for patriotic and nationalistic reasons, though it is still known by its original name in Sweden and by Swedish-speaking Finns. Due to its strategic geographical location, it sometimes used to be known as Gibraltar of the North.

The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North and Central European Plain.