Ons' Lieve Heer op Solder (OLHOS; English: Our Lord in the Attic) is a 17th-century canal house, house church, and museum in the city center of Amsterdam, The Netherlands. The Catholic Church was built on the top three floors of the canal house during the 1660s. It is an important example of a "schuilkerk", or "clandestine church" in which Catholics and other religious dissenters from the seventeenth century Dutch Reformed Church, unable to worship in public, held services. The church has been open as a museum since 28 April 1888, and has 85,000 visitors annually.