The underground cities that have been discovered around europe and even parts of the americas (such as out west) have always been so interesting to look in to. When you look at the amount of area that was cleared out, and even the details of what was chiseled into the rock faces, within each cave 'room', you begin to even put together the purpose of the rooms. Some room's in the famous underground cavern 'city' had chambers for domesticated animals... think about that. Think about how long it took to excavated that stone, with the tools of their time, and why they did it. WHAT was on the surface of earth, which could've been SO DANGEROUS, that people had to go underground for long periods of time???