Catholic mass was outlawed after 1578 when the city transferred to Protestant hands. However, city officials were tolerant of private Catholic worship if it was kept hidden. Therefore, in 1661, a wealthy Catholic merchant bought a stately canal house and included a Catholic chapel in his property. This charming chapel, Our Lord in the Attic, occupies the top floor of the canal house and served as a parish church for 200 years for Catholics living in the city center.