The white neoclassical cathedral on top of the broad flight of granite steps above Senate Square. Begun in 1830 to Carl Ludwig Engel's design and finished, with substantial modifications, in 1852. The interior is far plainer than the exterior promises — Lutheran restraint, white walls, organ — but the views from the steps over Senate Square, the harbour, and across to Suomenlinna are the obligatory Helsinki photograph.
Free to enter. The crypt below is sometimes open for temporary exhibitions; check the cathedral website.