The Marienkirche, completed in 1388 as a Dominican monastery church, is Bad Mergentheim's oldest significant building and contains one of the most complete collections of medieval frescoes in the region. The church has a solemn Gothic interior lightened by the warm colours of the surviving paintings, which date mainly from the 14th century.
The building survived the Reformation largely intact, which is not typical for this part of Germany, and the frescoes are correspondingly well-preserved. Even visitors with no particular interest in medieval religious art tend to linger here — the paintings have an immediacy that centuries of church whitewash have erased from most comparable buildings in the area.