Gulf of Finland National Park protects the outer archipelago east of Kotka, where forested islands, bare skerries, birds, and military history sit out in the Baltic wind. It is not a casual walk-from-town park; the point is getting onto the water and seeing the seaward side of Finland's southeast coast.
For independent travellers, the practical challenge is access. Boat services, guest harbours, and weather decide what is realistic, so plan ahead rather than turning up in Kotka and hoping for the best. If you can reach the islands, the reward is a very different landscape from the city's parks and maritime museums.