Derinkuyu, an underground Turkish city

In 1963, a resident of Nevsehir Province, Turkey, found a mysterious room behind a wall in his house. Further digging revealed access to a tunnel system extending to a depth of approximately 60 meters and large enough to shelter   as many asas much as  20,000 people together with their livestock and food stores.
This underground city, known as Derinkuyu, is   as large aslarger than  any underground complex ever found. Derinkuyu had   many moremuch more  amenities than other underground complexes, however. Like other underground systems, Derinkuyu contained items like wine and oil presses, stables, cellars, storage rooms, refectories and chapels. In addition to these items, however, it was   more elaborateelaborater  than other complexes because it   had more levelshad greater levels  and it contained a religious school and a cruciform church on the lowest (fifth) level.
It is believed that Derinkuyu was built some time during the 8th-7th centuries BC by the Phrygians and fully formed during the Byzantine era when it was used as protection from the Muslim Arabs during the Arab-Byzantine wars (780-1180). Derinkuyu is believed to have been inhabited   a lot longervery longer  than other complexes, too. Historians believe Derinkuyu was abandoned in 1923 when the Christian inhabitants of the region were expelled in the population exchange between Greece and Turkey. In excess of 200 underground cities containing a minimum of two levels have been discovered in this region of Turkey to date.