Białystok has one of the largest Orthodox populations in Poland — roughly a tenth of the city is Orthodox — and the Cathedral of St. Nicholas, completed in 1846, is the centre of its religious life. The exterior is a classic Russian Revival design with a tall central drum and onion dome, but the real attraction is inside.
In the 1900s the painter Mikhail Avilov was commissioned to fresco the entire interior in imitation of the Cathedral of Christ the Saviour in Kyiv. The result — saints, scenes, and a vast Christ Pantocrator in the dome — is one of the most accomplished pieces of religious art in northeastern Poland. Visitors are welcome between services; head coverings are appreciated.