Medieval Naantali grew up around the Catholic Convent of the Order of Saint Birgitta, which was dissolved after the 1527 Reformation. Towering above the harbour, the massive Convent Church, completed in 1462, is all that remains; its baroque stone tower dates from 1797. Archaeological digs have unearthed some 2000 pieces of jewellery, coins and relics now in the Naantali Museum.

At 8pm on summer evenings a trumpeter plays vespers (evensong) from the belfry; there are also regular organ concerts.