The Derinkuyu Underground City ( Cappadocian Greek : Μαλακοπή Malakopi ; Turkish : Derinkuyu Yeraltı Şehri ) is an ancient multi-level underground city in Derinkuyu County, Nevşehir Province , Turkey . It is up to 85 metres (279 ft) deep, large enough to house 20,000 people along with livestock and food stores. It is the largest excavated underground city in Turkey and one of several underground complexes found throughout Cappadocia .

The Derinkuyu underground city could be closed from the inside by large stone doors. Each level could be closed off separately. It could accommodate up to 20,000 people with amenities found in other underground complexes throughout Cappadocia, such as wine presses , oil presses , stables , wine cellars, storehouses, refectories, and chapels . Unique to the Derinkuyu complex is a spacious room on the second floor with a barrel-vaulted ceiling. It is reported that this room was used as a religious school and the rooms to the left were for studies.  Starting from the third and fourth floors is a series of vertical stairs leading to a cross-shaped church on the fifth floor, which is also the deepest level in Derinkuyu. The large 55-metre (180 ft) ventilation shaft appears to have been used as a well. It supplies all the water to the people on the upper floors.

According to the Turkish Ministry of Culture, the cave system may have been originally built by the Phrygians in the soft volcanic rock of the Cappadocia region in the 8th–7th centuries BC.  When the Phrygian language disappeared during the Roman period , replaced by the Greek language ,  the people, now Christians, expanded their caves, deepening the structure to several levels and adding Greek chapels and inscriptions . 

The city at Derinkuyu was fully formed during the Byzantine period, when it was used extensively for protection against Arab Muslims during the Arab-Byzantine Wars from 780 to 1180.  It was also connected to other underground cities through many kilometers of tunnels. Some of the artifacts discovered in these underground settlements belong to the Middle Byzantine period , between the 5th and 10th centuries. These underground cities continued to be used by native Christians for protection against invasions by Timur ‘s Mongol army in the 14th century. 

After the area fell into the hands of the Ottomans , the cities were used as refuges by the natives against the Turkish Muslim rulers. 

As late as the 20th century, the local population, the Cappadocian Greeks, were still using underground cities to escape persecution. For example, Richard MacGillivray Dawkins , a Cambridge linguist who conducted research from 1909 to 1911 on the native Cappadocian Greek-speaking people of the region, recorded an incident that occurred in 1909, “When news of the recent mᴀssacre at Adana arrived, a large number of the population of Axo took refuge in these underground chambers, and for several nights they did not venture to sleep above ground.