Hello @EmirOzyasar
I have to say that I thoroughly enjoyed your post and photos. I went into the eight-story Derinkuyu underground city and just could not comprehend the size, scope and ingenuity of the construction. I went down into the city from a small hardly visible opening in an open field. They even had rooms for their animals and the ventilation system throughout was incredible to say the least! I recall and have photos of the large stone circular disks that you mention and that were rolled over the tunnel entrances to close off the tunnels for security. A visit to this well preserved historical place is highly recommended.