Back in 1963, a resident of the Nevşehir Province of Turkey found a secret room behind one of his walls. This room led to a tunnel, which led to one of the most shocking discoveries of the 20th century.
The tunnel led to the ancient underground city of Derinkuyu.
Derinkuyu is not the oldest nor is it the largest underground city. However, at 18 stories deep, it is the deepest.
The city was used as a bunker during natural disasters, or times of war. The water wells are not attached to the surface, so they cannot be poisoned from above by enemies.
The city had shops, tombs, schools, livestock, and individual homes.
Archaeologists have been studying this discovery for over 50 years now, and it has provided them with some crucial insight of the ancient world.