The Church of St. Casimir on Didžioji Street is the oldest Baroque church in Vilnius, built by the Jesuits between 1604 and 1618. St. Casimir was a 15th-century Polish-Lithuanian prince who died young and was canonised, becoming Lithuania's patron saint. The church was dedicated to him, though it has had various other uses over the centuries including as a granary under Napoleon and as a museum of atheism during the Soviet period.
The interior is relatively restrained by Baroque standards, with a distinctive crown-topped dome that is visible from several points in the old town. The three-handed portrait of St. Casimir — a 16th-century painting hanging in a side chapel — draws pilgrims and the curious in equal measure. The church is active and holds regular services; visitors are welcome outside service hours.