The Phyrigians not only included Midas, Croesus, and the Gordian knot.
And in 700 BC or so they built a large underground city that could house 30 thousand folks.
It is unknown why Derinkuyu was created. The huge stone doors and access to water may have meant that it was designed to be a stronghold should the Phrygians be attacked. The presence of churches and other religious buildings also suggested that the complex may have been used for religious purposes. Only about ten percent of the stronghold has been excavated and so scientists are still learning more about the structure as they go along. It is believed that while the city may have been started in the 8th to 7th centuries BCE it may have been expanded and enlarged during the Byzantine era.
the city goes 11 stories deep.