This building in the middle of the old centre, at Oudezijds Voorburgwal 40, doesn’t stand out. But a great secret is hidden behind its façade. If you climb the narrow stairs and pass its age-old rooms, you will discover a real church in the attic. Complete with beautiful statues, decorated columns, and a large organ. The church has a very old-fashioned Dutch name, Ons’ Lieve Heer op Solder (Our Dear Lord in the Attic). It was secretly built at a time when religious people in Amsterdam still had a lot of quarrels with each other. The Protestants won that battle and said Catholics were no longer allowed to hold Mass in public. A rich Catholic merchant, Jan Hartman, didn’t want to give in to that and started building his Schuilkerk (hidden church) in 1630. Ons’ Lieve Heer op Solder is now a museum; you enter the building through an underground passage at number 38.