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Kansalliskirjasto
Photo: Eteil, CC BY-SA 4.0 via Wikimedia Commons
The beautiful National Library has books all the way from the early 19th century accessible for everyone (and books older than this are kept away from the public). The picturesque building with its glamorous stone columns is definitely worth a visit.
© OpenStreetMap contributors
Tuomiokirkko
The unofficial symbol of the city, this striking white cathedral dominates the central Senate Square. Based on designs by Carl Ludvig Engel and completed in 1852, the cathedral has been refurbished, and the 12 Apostles are on the roof looking down at the world below. While entry is no longer free, one might argue that the building is more impressive from the outside anyway.
A museum about money and banking, as the name reveals.
The museum covers a whole series of old buildings around Helsinki, but the centrepiece is the (short) street of Sofiankatu itself, carefully restored as a replica of the 1930s.
Uspenskin katedraali
A classical and prominent onion-domed Russian church, the largest Orthodox church in Western Europe, Uspenski Cathedral serves Finland's small Orthodox minority. The name comes from the Russian uspenie, from the Dormition (death) of the Virgin Mary. The five domes are topped with 22-carat gold, and some of the icons within are held to be miraculous.