Cappadocia Underground Cities

http://www.turkeytravelplanner.com/go/CentralAnatolia/Cappadocia/yeralti/index.html
 Derinkuyu is situated on Nevsehir-Nigde roadway - 30 km to the south of Nevsehir.

Carved from the living rock, Derinkuyu is one of five inter-connected underground complexes with a total estimated capacity of 100,000 people.

The historical region of Cappadocia where Derinkuyu is situated, contains several historical underground cities, carved out of a unique geological formation, many of which were largely re-used by early Christians as hiding places.

Over 200 underground cities at least two levels deep have been discovered in the area between Kayseri and Nevsehir, with around 40 of those having at least three levels. The cities at Derinkuyu and Kaymaklı are two of the best examples of underground dwellings.
http://www.ancient-wisdom.co.uk/turkeyderinkuyu.htm