After reforms were made to the city in the 17th century, the Protestant Dutch government formally outlawed Catholicism, forcing Catholics to practice their religion secretly. This led to the construction of secret Catholic churches all over Amsterdam, including a chapel in de Wallen, known as Ons' Lieve Heer op Solder, which was hidden inside the top floor of a canal. the channel. This narrow, secret sanctuary somewhat survived this turbulent period and at the end of the 19th century it was turned into a wonderful museum.