The Orthodox Church of St Nicholas is one of Kotka's most atmospheric historic buildings, a stone church from the period when Ruotsinsalmi was a Russian fortress town. Its neoclassical exterior is modest but elegant, and the setting in Isopuisto gives it a calm pocket of space in the centre.
It is worth seeing because Kotka's identity is tied to sea power, borders, and the shifting Russian-Finnish history of the Gulf of Finland. Step inside if it is open, but even from the park the church gives a useful historical anchor to a city better known for maritime museums and parks.