Derinkuyu (Turkish for deep well/shaft, former name Malakopía,[2]) is, along with Kaymaklı, the most famous of the underground cities in Cappadocia and is located in the town of the same name. This is located in the Turkish province of Nevşehir, 29 kilometers south of the provincial capital. In addition to Derinkuyu, there are believed to be over 50 underground cities in Cappadocia; 36 have been discovered so far, but only a few have been made available to the public. Derinkuyu is the largest accessible facility.
Source: Wikipedia
Ice-cold shivers accompany you during your visit, considering how people and animals fled from enemies in this underground fortress.