Suomenlinna Sea Fortress, also known as Sveaborg, is a historic sea fortress located just 4 km southeast of Helsinki, Finland. Built in 1748 under Swedish rule to defend against Russia, it surrendered during the Finnish War in 1808. The fortress served as a base for the Baltic Fleet under Russian rule and was later renamed Suomenlinna after Finland gained independence in 1917. Today, it's a popular spot for picnics and exploration, boasting UNESCO World Heritage status since 1991. With its picturesque setting and rich history, Suomenlinna is a must-visit destination for tourists and locals alike.