We know that Cappadocia has many mysteries under the ground. Underground cities of Cappadocia are so huge that even today a few parts of those ones are open to visit or unearthed. They are also so deep that we could unearth nearly half of them.
Derinkuyu underground city which is one of them has so great feature that it may shock you. The depths of the undergound city was used as mental hospitals. Absolutely they are the oldest mental hospitals of the world. Sick people were put in the rooms and probably they were left for death. It is terrifying. Today we can go down around 3 km. depth of the underground city but it is deeper than it.
A community was living in this underground city (it is guessed that there are more than 100 underground cities under Cappadocia). So we can see everything on social life of this community in this structure. Kitchens, rooms for sleep and toilet levels are the outstanding features. The passages are so tiny that only one person can move in.