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.

Helsinki is the capital and most populous city in Finland. It is located on the shore of the Gulf of Finland and serves as the seat of the Uusimaa region in southern Finland. Approximately 675,000 people live in the municipality, with 1.25 million in the capital region, and 1.58 million in the metropolitan area. As the most populous urban area in Finland, it is the country's most significant centre for politics, education, finance, culture, and research. Helsinki is situated 80 kilometres (50 mi) to the north of Tallinn, Estonia, 360 kilometres (220 mi) to the north of Riga, Latvia, 400 kilometres (250 mi) to the east of Stockholm, Sweden, and 300 kilometres (190 mi) to the west of Saint Petersburg, Russia. Helsinki has significant historical connections with these four cities.