The Church of the Holy Cross is a late-medieval fieldstone church on the northern edge of Old Rauma — the only intact pre-Reformation Franciscan church in Finland. Built around 1510 as part of a friary complex, it survived the dissolution of the monastery, several town fires, and centuries of use as the parish church. The exterior is austere granite with stepped gables; the interior is a single tall hall with whitewashed walls and a remarkable set of restored medieval wall paintings.
The paintings, rediscovered in the late 19th century under layers of plaster, depict biblical scenes in a naïve Northern European style — angels, apostles, and an unusually detailed Last Judgement. The pulpit and altarpiece are Baroque additions. The church is still in regular use for Lutheran services and concerts, and the acoustic is excellent. A small graveyard wraps the building. Admission is free; opening hours are short outside summer.