Özkonak Underground City

While the exact age of the Cappadonian underground city of Özkonak is unknown, it dates back to before antiquity however the industrial systems laced throughout its halls seem surprisingly advanced, especially the hot oil holes sitting above each entrance which seem positively medieval. 

Discovered in 1972 by a farmer who noticed the water he would give to his crops seemed to mysteriously drain somewhere into the ground, Özkonak was found to be one of three expansive underground strongholds in the region (including Kaymaklı and Derinkuyu). Each of the cities featured multiple, stacked levels of dug out chambers connected to a shockingly sophisticated ventilation and water system. Özkonak differs from its sister cities in two important aspects however.

Across Özkonak's ten descending levels, there was a crude communication system installed so that each level could talk to the one above or below it, a feature that is unique to the city. Also unique to the city, is its system of holes just above the entrances to the city through which they could pour hot oil on any attacking forces. Medieval castles eat your heart out.

Four of Özkonak's ten floors are open to the public so that visitors can get a taste of what life's like underground. Just look out for falling oil.