The Largest and Deepest Underground Cities in the world.

Derinkuyu, an underground city thousands of years old, seems to be a world of its own. Carved into soft volcanic rock known as tuff, Derinkuyu creates a stunning underground city. This city is known for its extensive and complex underground city system, so experts estimate that this city can accommodate around 20,000 people. https://www.febspot.com/yans/