A Man Knocked Down His Basement Wall, Discovering Ancient Underground City That Housed 20,000 People (Video & Pictures)

Researchers believe Derinkuyu was originally used as a storage space before it became a bunker to hide from invaders. The doors connecting each level were blocked by half-ton boulders only moveable from the inside that contained a small hole that allowed residents to spear the confined trespassers. The city was likely originally used to store goods but was then used as a bunker to escape from foreign invaders — the dimly lit hallways were intentionally built narrow and low so intruders would be forced to stoop and enter in single file.