Fortress islands – the military history of the Gulf of Finland by boat
The islands of the Gulf of Finland have fortifications ranging from 18th-century sea fortresses to coastal artillery fortresses that remained in operation into the 2010s, and many former fortress and military islands are now open to everyone. On this page we have gathered nine fortress and military islands from Ekenäs to Hamina, together with tips for planning your trip.
Details checked against sources in October 2026.
Why go to the fortress islands?
On the fortress islands you can see nearly three centuries of coastal defence history. In 1748 the Swedish Crown began building Suomenlinna and Svartholma to defend the eastern border, and in the 1790s Russia built Fort Elisabeth on Varissaari as part of the Ruotsinsalmi sea fortress. The Russians began fortifying Rankki during the First World War, construction work on the Kirkonmaa fortress started in 1927, and the fortification of Ulko-Tammio began shortly before the Continuation War, in 1941.
Many of the islands were closed military areas for a long time. Rankki was closed to civilians for about a hundred years, Vallisaari and Kuninkaansaari were opened to visitors in 2016, and the Kirkonmaa fortress was closed down at the end of 2013. In places, long military use has kept nature exceptionally diverse: Vallisaari proved to have the richest flora of the more than 200 islands surveyed in Helsinki.
As destinations, the fortress islands vary a great deal. Suomenlinna has museums and cafés, Jussarö and Rankki have a restaurant and a sauna, and Svartholma has an exhibition and a summer restaurant. Pirttisaari and Ulko-Tammio have few services, and the day is built around walking, nature and your own picnic.
Fortress islands from west to east
Here we have gathered nine fortress and military islands, each with its own trip guide on our site. In the guides you will find the routes, harbour details and services.
West Uusimaa
JussaröA former mining and military island in the outer archipelago of Ekenäs, partly within Ekenäs Archipelago National Park. After the mine closed, the island was taken over by the Finnish Defence Forces, and the Finnish Border Guard's coast guard station operated on the island until 2011. The nature trails run past old mine shafts, and the island has a guest harbour, a restaurant and a sauna.
Helsinki region
SuomenlinnaAn 18th-century sea fortress and UNESCO World Heritage Site off Helsinki. The guest harbour is next to the dry dock, and from there you can walk to the ramparts, museums and cafés. Mooring is subject to a fee, even for a short day visit.
Helsinki region
VallisaariSuomenlinna's neighbour on the other side of the Kustaanmiekka strait. The island's best-known sight is the Aleksanterinpatteri battery, built after the Crimean War, which has a viewing platform on its roof. Keep to the marked routes, as there are dangerous structures off the routes and there may still be explosives in the ground.
Porvoo–Loviisa
PirttisaariAn island in the outer Porvoo archipelago that was a fortress island of the Finnish Defence Forces in the 20th century. The island still has three coastal guns, bunkers and a fire control tower. There is a campfire site and a toilet near the Svartviken jetty, but there is no well, so bring drinking water with you.
Porvoo–Loviisa
SvartholmaSuomenlinna's sister fortress at the mouth of Loviisa Bay. A British naval squadron blew up the fortifications during the Crimean War in 1855, and the Finnish Heritage Agency restored the fortress over a period of about 30 years. The island has a free exhibition and a summer restaurant, and the guest jetties on the east shore are free of charge.
Kotka–Hamina
VarissaariA fortress island off Kotka. Fort Elisabeth was built in 1790–1796 as part of Russia's Ruotsinsalmi sea fortress, and an Anglo-French fleet destroyed the fortifications during the Crimean War in 1855, but the ruins of Fort Elisabeth can still be seen. The island has a summer restaurant, and the journey from Sapokka is short.
Kotka–Hamina
RankkiA fortress island off Kotka that was closed to civilians for about a hundred years. On the island you can see heavy coastal guns and a wooden barracks for the rank and file from the Russian era, and Restaurant Sotku operates in the former soldiers' home.
Kotka–Hamina
KirkonmaaAn island off Kotka with a coastal artillery fortress that operated in its southern part until 2013. In the Winter War, in March 1940, the Kirkonmaa and Rankki batteries together repelled an attack made across the ice. The summer café Rantabaari Knaapi operates near the guest harbour.
Kotka–Hamina
Ulko-TammioAn uninhabited island in the Eastern Gulf of Finland National Park in Hamina's outer archipelago. The war history trail runs past restored guns, information boards and a tunnel cut into the rock, and there is an observation tower in the middle of the island. No food is available in the national park and there are no waste bins, so bring a picnic and take your rubbish away with you.
Opening hours, harbour fees and services vary by season. Check them on the destination's own website before you set off; you will find the links in each destination's trip guide.
Military history in these guides too
- Hamina: Hamina is a town laid out inside a star-shaped fortress built in the 18th century.
- Loviisa: East of the centre of Loviisa you can still see the Rosen and Ungern bastions of the 18th-century border fortress.
- Gunnarsörarna: The trenches of an anti-aircraft battery have survived on the island's highest rock.
- Pihlajasaari: During the First World War, light fortifications were built on the islands, and along the trail you can see old fortifications.
Getting around the fortress islands
The fortress islands have old military structures, steep drops and rocks. Keep to the marked routes and follow the destination's instructions: on Vallisaari, for example, there are dangerous structures and places at risk of collapse off the routes, and on Pirttisaari the gun positions, bunkers and fire control tower may only be viewed from the outside.
Making fires is restricted. Fires are completely prohibited in Suomenlinna and on Vallisaari and Kuninkaansaari, and on Svartholma, Pirttisaari and Ulko-Tammio, for example, fires may only be made at sites designated for the purpose. The rules are stricter when a wildfire warning is in force, so check the destination's instructions before you set off.
The shore rocks can be slippery, and the Kotka archipelago is a tick risk area. Wear sturdy shoes, stay on roads and paths, and check your skin after the trip.
Agree on refuelling with the boat's owner before you set off, and keep an eye on the wind forecast throughout the day, especially if you are heading to the outer archipelago.
What to bring?
- Sturdy shoes with a good grip for the rocks and paths
- A picnic and drinking water, especially for destinations without services
- A rubbish bag, as many of the islands have no waste bins
- A charged phone kept somewhere dry
Shall we head to the fortress islands?
Rental boats on the Gulf of Finland are listed on Friilo. Choose the area you want to set off from, and arrange the boat pick-up and refuelling with the boat's owner.