Most buildings in the world are built upwards: you start at the ground and add stones, bricks or wood until you reach the top. The churches at Lalibela are different. The builders started with a solid rock hill, drew the shape of a church on the top, and then dug down all around the outside, leaving the church standing in a giant pit.
Then they hollowed it out from the inside, carving doors, windows, columns and arches out of the same single piece of rock. Every single church at Lalibela is one whole stone. There are no joins anywhere.
The most famous one is called Bete Giyorgis - the Church of Saint George. From above, it is shaped like a perfect cross. It is about 25 metres tall, carved down into the ground. You walk to it through tunnels and steps cut into the rock.
Lalibela is a UNESCO World Heritage Site - the world has agreed it is important for everyone. People still visit the churches today and use them, exactly the way people did 800 years ago.