At Prinsengracht 7 used to be a clandestine Catholic church called the Posthoorn.
After the reformation, the alteratie (alteration) 1578, Catholic churches in the Netherlands were forbidden any outward appearance of a Catholic Church. People had to worship in “hidden” churches within houses.
The old brown cafe from 1642 Papeneiland 'hides'
in her cellar an old escape route for Roman Catholics (Papen). Their
ceremonies used to be forbidden.
Exit of the escape route from Prinsengracht 7 to the cellar of brown cafe Papeneiland at Prinsengracht in Amsterdam