Derinkuyu Underground City in Cappadocia Turkey,
The first two stories contain kitchens, storage chambers, bedrooms, dining halls, wine cellars, stables, and toilets, whereas the third and fourth stories consist of places of hiding, churches, armories, and tunnels. The tunnels form connecting links with some underground cities near Derinkuyu so that the population could save their lives by using these escape routes. We have reason to believe that one of the tunnels on the third story is connected with an underground city at Kaymakli 9 km. away. The tunnel in question is wide enough for three or four people to walk upright side by side. The ventilation ducts of the tunnel, many of which have been filled with rubble or destroyed through the years, are expected to be opened in the coming years.
Certain clues indicate that the lower floors of the underground city were places of refuge. One of these is the existence of stone doors in the corridors, which must have been closed against the attackers after the inhabitants had escaped there. These stone doors could only be opened and closed from the inside, and against them, the invaders would be helpless. They have holes in the middle which may have been used in defending the place. The lower stories have wells, escape ducts, a church, a meeting hall, a dungeon, graves and ventilation ducts. Derinkuyu has 52 such ventilation ducts; because of the sloping terrain on which the town is built, their length varies from 70 to 85 meters. The name Derinkuyu (deep well) is derived from the many wells on the bottom level. Its old name Malagobia means “difficult subsistence.”
Until 1962 the water supply of Derinkuyu was provided from these wells with hand turned wheels; since then some wells have had motor pumps installed and the town still depends on them for its water. Only on the first story, the air ducts number is about 15.000.