However, I could not have been more wrong. Underground cities have existed within our real world. And I'm not talking about a few caves carved into the side of a mountain either, I mean real cities that go deep beneath the earth.
This underground city has 4 levels and nearly 100 tunnels with various rooms off of them. This one was also meant to be lived in and included stables (on the first level), a church, storage, dwellings, a wine press, and a copper smelting area.
The region where these two underground cities can be found has over 200 underground cities each with a minimum of 2 levels; 40 of these have a minimum of at least 3 levels. Many of these are open to the public, though not all of the cities have been fully explored. To know that there really do exist underground cities is fascinating.