Suomenlinna is a sea fortress built on six islands at the entrance of Helsinki’s harbor. The fortress is an interesting example of European military architecture of the time. It has served to defend three different sovereign states over the years: the Kingdom of Sweden, the Russian Empire and most recently the Republic of Finland (after gaining its independence in 1917).
A special Soumenlinna postmark! The name of the fortress under Swedish rule was Sveaborg. The Finnish name until 1918 was Viapori.