Okay kiddo, have you ever seen a hole in the ground? Maybe you made one while you were digging in the sand or dirt. Now imagine that someone dug a hole in the ground that was bigger and deeper, maybe as big as your bedroom!
Next, picture a roof on the ground above the hole. It's like a house, but upside down! This is what we call a pit-house.
Long ago, people used to build these kinds of houses so that they could stay warm in the winter. Because the pit-house is underground, it's much warmer than a normal house. People could light fires inside and the smoke would go up through a hole in the roof.
Some people still build pit-houses today, especially in places where it gets very cold or very hot. They can be cozy and comfortable, just like a regular house, but they're a little bit different since they're built into the ground.