A schuilkerk, which is Dutch for "hidden church," is a type of church that was created in the Netherlands during the time when people weren't allowed to practice their own religion freely.
Imagine you want to go to church to pray, but someone tells you that you can't because the government says you have to believe and worship a certain way. That's what happened to a lot of people in the Netherlands a long time ago.
So, some people got creative and made secret churches that were hidden from the government. They would use houses, warehouses, and other buildings to secretly hold services without anyone knowing. They even made the entrances look like regular buildings so nobody could tell what was really going on inside.
These hidden churches allowed people to worship in peace and practice their own religion without being punished. After a while, the government became more tolerant and people were allowed to build real churches again, but the schuilkerk played an important role in history by providing a safe place for people to practice their faith.