Suomenlinna comprises eight islands with a total land area of about 80 hectares. However, Suomenlinna is not just islands—it is also water. In fact, the maritime area of the fortress is as extensive as its land area. Beneath the surface lies a completely different world: the underwater Suomenlinna. The waters around the fortress contain around 80 underwater archaeological sites and other underwater remains, including various finds. Together with the natural marine environment, they form a distinctive and unique underwater cultural landscape.

Historically known as Viapori, Suomenlinna was a sea fortress and naval base, as well as an urban center for thousands of people, both soldiers and civilians. For centuries, maritime traffic around the islands and harbours has been active. The fortress hosted all sorts of vessels, from the boats of freight rowers and residents’ daily transport to large warships, both made of wooden and iron. Therefore, about half of the underwater archaeological sites at Suomenlinna consist of ship and boat wrecks. Some of these wrecks ended up on the seabed due to accidents or negligence, while others were deliberately sunk.

Over the centuries, the fortress was built, equipped, and developed according to the warfare methods, tools, and needs of each era. Shores were fortified, waters dammed, islands connected, and routes closed. The fortress has housed docks and shipyards, leaving traces beneath the waves. These traces include grand and imposing structures as well as smaller, timeworn underwater remnants from different historical periods. Also, military actions have left their mark beneath the surface of Suomenlinna.

This tour takes you deeper into the underwater cultural heritage of Suomenlinna. The selected highlights include well-documented shipwrecks and intriguing underwater structures that shed light on the history of the fortress from an underwater perspective.