Imagine a big building called a "church" where people go to talk to God and pray. In Sweden, some of these churches have very old paintings on the walls and ceiling called "frescos". These paintings show pictures of people from the Bible, like Jesus and his friends, doing different things like cooking or praying.
The painters would mix special paints with water and then put the paint on the wall while it was still wet. This made the colors very bright and beautiful. The paintings were often done by very talented artists who knew how to make the people and scenes look very realistic.
But because these frescos are so old, they can sometimes start to fade or peel off the wall. It's important to take care of them by not touching them or using harsh chemicals to clean them. That way, people can still admire and learn from these historic paintings for many more years to come.