The Orthodox Cathedral in the center of Helsinki. A magnificent observation deck, for the sake of it alone it is worth climbing the stairs. Inside, the cathedral is not so amazing, as a concession, believers are allowed to sit during the sermon. You need to visit.
The main Orthodox church of Finland, the Cathedral of the Helsinki Metropolitanate. It is located on a cliff in the Katayanokka area. A holy place of prayer. An uninhabited atmosphere.