Below is a History Channel program on Derinkuyu the ancient underground city of Cappadocia.

Some believe that Derinkuyu was first built around 800 BC by the Phrygians with others attributing the city’s origin to the Hittites who may have built this in 1000 BC or earlier.

As noted by David Wilcock, the city’s origins may be even earlier and related to the ancient Persian Zoroastrian tradition. Giorgio A. Tsoukalos  notes that in the ancient Zoroastrian Vendidad, legends exist of how Ahura-Mazda (the single ominipotent god of the Zoroastrians) instructed Yima to build an underground refuge very similar to that seen in  Derinkuyu.

For more information, see the video below:

Derinkuyu the Underground City