In 1963, a Turkish man in the region of Cappadocia was making improvements to his home when he made an incredible discovery.

After knocking down a wall in his basement, he stumbled upon a secret room, which led to an underground tunnel, which opened up into a completely hidden ancient city: Derinkuyu.

Photos of the preserved city reveal how 20,000 people - including livestock and entire food supplies - could have lived 18 storeys beneath the earth.

Thought to have been created during the Byzantine era in 780-1180AD, the network of kitchens, stables, churches, tombs, wells, communal rooms and schools was most likely used as a massive bunker to protect inhabitants from the Arab–Byzantine wars or natural disasters.

During this time, cave-like chapels and Greek inscriptions were added to the ancient city, and about 600 entrances allowed people to come and go. 

Heavy stone doors could close Derinkuyu from the inside in order to fend off intruders, and each storey could be shut off individually.