In 1963, a man in the Nevşehir Province of Turkey knocked down a wall of his home. Behind it, he discovered a mysterious room and soon discovered an intricate tunnel system with additional cave-like rooms. What he had discovered was the ancient Derinkuyu underground city in Turkey.
The elaborate subterranean network included discrete entrances, ventilation shafts, wells, and connecting passageways. It was one of dozens of underground cities carved from the rock in Cappadocia thousands of years ago. It remained hidden for centuries.
The underground city at Derinkuyu is neither the largest nor oldest, but its 18 stories make it the deepest.
The city was most likely used as a giant bunker to protect its inhabitants from either war or natural disaster.
It had access to fresh flowing water -- the wells were not connected with the surface to prevent poisoning by crafty land dwellers. It also has individual quarters, shops, communal rooms, tombs, arsenals, livestock, and escape routes. There's even a school, complete with a study room.