Okay, so have you ever seen a big house made out of stones? That is called a chysauster. It is a special type of house that was built a long time ago in a place called Cornwall in England.
Chysausters were built by people who used to live there a really long time ago, before we were born. They used to build these houses to protect themselves from their enemies who wanted to hurt them.
Chysausters are special because they are built in a way that makes them really hard to see from far away. They have walls made of stones and are built in a special way that makes them very strong. There are usually lots of rooms inside a chysauster for people to sleep, cook and eat.
Even though people don't really use chysausters anymore, they are still very important to learn about because they tell us about the history and how people lived a long time ago.