Suomenlinnan Kirkko Helsinki

Built by the Russians in 1854 for their garrison on Suomenlinna, this church originally had five onion domes, and served as an Orthodox place of worship until the 1920s, when it became Lutheran. The interior is stark and unadorned, and it’s one of the few churches in the world to double as a lighthouse – the beacon was originally gaslight, but it is now electric. Mass is celebrated (in Finnish) at 2pm on the first Sunday of the month.