Derinkuyu Underground City

verifiedAskCappadocia says

Derinkuyu is the deepest of Cappadocia's underground cities, descending some eight levels and once capable of sheltering thousands of people along with their livestock. We picked it for the sheer scale and the engineering: ventilation shafts that still draw fresh air, a deep well, communal kitchens, a church and the famous rolling stone doors that locked each floor from the inside. Part of the UNESCO landscape, it's a genuinely jaw-dropping feat of ancient survival architecture. Go with a guide to understand what you're seeing, bring a layer for the cool air, and be honest with yourself about the steep, narrow, low descents if you don't love enclosed spaces.