Round stone door inside underground city at Derinkuyu.
The underground cities were built by the Christians to escape persecutions from the Persians and Arabic armies during the 6th and 7th centuries. The Derikuyu city was carved eight levels deep into the earth. The passage ways connecting the rooms are narrow and small, and the experience of visiting the city can be quite claustrophobic. During my visit, I noticed that a few tourists had to prematurely stop their tour and get back to the surface.