Carved deep into the soft volcanic ash landscape of Central Anatolia, the ancient underground cities of Derinkuyu and Kaymakli once sheltered tens of thousands of inhabitants from invasions. Extending up to 85 meters below the Earth's surface across up to 18 distinct levels, these subterranean complexes required reliable airflow, temperature regulation, and smoke removal to sustain human life for extended periods. To solve this, ancient Hittite and Phrygian engineers developed a sophisticated passive ventilation system relying on natural thermodynamic principles.
The primary engine of this system consisted of vertical ventilation shafts, some plunging over 55 meters deep, directly connecting the lowest levels to the surface. Branching off from these main conduits were thousands of smaller, interconnecting air channels that reached individual living quarters, stables, kitchens, and storage rooms. The system harnessed thermal stack effects and micro-pressure differentials.
As human body heat, cooking fires, and lamps warmed the air inside the lower rooms, the buoyant warm air rose through secondary ducts. This thermal updraft created a gentle low-pressure vacuum that continuously pulled cooler, denser fresh air down through the primary central shafts. Additionally, the surrounding porous tuff rock served as an immense geothermal heat sink, maintaining a steady year-round temperature between 12 and 15 degrees Celsius regardless of scorching Anatolian summers or freezing winters.