Cities of the underworld are really old cities that were built a long, long time ago under the ground. People built these cities for different reasons, like to hide from enemies or to protect themselves from the weather.
Imagine you have a secret hiding spot under your bed where you can go and nobody can find you. Well, cities of the underworld are like that, but for adults a long time ago. These cities are made out of tunnels and rooms that people dug out of the earth.
Some cities of the underworld are really big and have lots of rooms, like a maze. People who lived there had to be careful not to get lost. Some cities of the underworld have been found in different parts of the world, like in Turkey, Iran or Italy.
City of the underworld are really fascinating to learn about because they remind us of how creative people can be, and all the amazing things we can do if we work together.