Imagine you have a secret hideout with a big fort made out of pillows and blankets that you built in your room. Now, imagine that people long ago also had secret hideouts or forts, but they didn't use pillows and blankets. They used stones, dirt, and wood to build their forts, which were called "burgstalls."
Burgstalls were built a long time ago in Europe, mostly in Germany and nearby areas. People back then would build them on hills, so they could see who was coming from far away. They built walls around the fort to keep themselves safe from enemies. They also built houses, where they could live, and a place for their animals, like cows and sheep.
Nowadays, people can visit these old burgstalls and see the leftover stones and walls. It's like going on a treasure hunt and finding clues about how life used to be a long time ago. It's a way to learn about the past and see how people used to live.