Isn't that place awesome? It's an excellent smack-down for folks that start prattling on about how dungeons are unrealistic.It's not the only underground city in turkey either, there's many of them and some go down over 8 levels seemingly with long connecting tunnels between some.
I noticed the same thing about Derinkuyu as well with another map of it in case you were interested.http://betweengoodandawful.blogspot.com/2011/07/real-life-urban-planning-as-dungeon.html
There's a book on Derinkuyu called Caves of God that I've been meaning to check out for a while, but have not gotten around to yet. There is also a great post about this on BLDGBLOG.