Although there are not many inscriptions and informations, it is believed that the city was commonly use in Byzanthion period which was also believed that people started to settle there in 3000 BC. Proto-Hittites period. It is also known that first christians who were running away from Romans persecution, came to Kayseri over mezapotamia and arrived in Cappadocia from Kayseri and took shelter in those underground cities (There are not only one underground city found around Cappadocia).
The entrances of those cities are well hidden and not easily found and also are not easily enter from the entrances even though it can be found. Those cities protected the first christians from the Roman soldiers and Arabic raiders for such a long time.
Today, only the first 8 floors are open for visitors and you can only reach for 50 meters depth. However, it is believed that it has 85 meters depth which is equal to 12-13 floors. Approximately, 50 Thousands of people were living in this city which has a perfect ventilating system. Since you need to pass through very tiny rooms to reach the 8th floor, it is suggested to the over weighted and clostrofobic people not to get in the city.
In the 3rd floor, you can find the school for missionary, the church in a shape of cross, confessionals and the cemetery. There is also a long tunnel where you can not see the end. If you wonder where this tunnel leads, it's believed that this tunnel which is about 2 meters high and quite similar with today's city underground metro tunnels, connects the city with other underground cities such as Kaymaklı.
It's also said that the oldest known mental hospital is located in this city. This city is quite similar with the piramids in Egypt in terms of their history and the mistery. There is a lot of question marks considering the end of the city is close to the center of the earth and if there was engineers to built this city. Although the first christians used these cities for the first time, there are no any information if they built the city. Erich Von Daniken who is a specialist author and famous with his book called "Chariots of the Gods", came to city to find out this mistery in 1982. According to his researches, he claims that the city was built for protection from the attacks coming from the sky and used as a shelter against the aliens invasion.
Interestingly, this theory is overlapping with the story "Angels coming from the sky" that the peasants are telling. According to story, in the very early times angels were living in Derinkuyu region. They arrived from the sky and found a country in this region. After a while, bad spirits also arrived from the sky here and started to bother this country. This fight between the angels and the bad spirits ended up after angels created this underground city and defected by using their magic. Again according to the peasants, in some nights, angels appear on the earth as light beams and yet continiue to live in those cities without showing theirselves to anybody.
Even though there are many sayings about Derinkuyu, there is one truth which is there are still a lot of unknown tracks, cities and misterious worlds.