Mankind has many tunnels and large cities miles below the surface of the Earth.
Most of us are not told about these cities, yet there are 100,000's of people down there.
Just relax with this knowledge and know that you will most likely never live there, and if you did, it may not be that much fun.
The airforce guys in the photo have a Laser Tunnel Boring Machine I think, yet not 100% certain that it is (no, it is just a normal tunnel boring, yet they do have Laser ones as well). If this is a nuclear powered laser borer, then it is above top secret, does not exist and will melt a kilometer of tunnel per day.