Aydıntepe Underground City The Aydıntepe underground city is a remarkable man-made structure located in the rural district of Bayburt Province, Turkey, about 25 km (16 mi) northwest of Bayburt, beneath residential areas. This ancient subterranean city is carved out of volcanic tufa-stone and boasts chambers, hallways, and halls without the use of building materials. The size of the chambers varies from 2-5 meters (6.6 ft.) below ground surface level, and their structure is self-supporting, meaning they don't need additional construction support. The small rooms are 1 meter wide by 2 meters high, and there are eight cone-shaped shafts placed over the hallway, most likely for observation or ventilation purposes. However, some entrances and structures are now inaccessible due to collapse or later construction. At the entrance of the underground city stands a round rock piece, 1.5 meters in diameter, that can close off the city from the outside when needed. The tombs above and figures inside indicate a history stretching back two millennia, from late Roman or early Byzantine times through Christian and Islamic rule. Underground cities served as a safe haven from persecution and war. Inside the city, there are cellars, storage rooms, water sources, and a pool. While in use, the underground cities were fortified and had a closing device and guard chamber integral to their structure.