Derinkuyu Underground City in Cappadocia, Turkey, is an extensive subterranean complex dating back to the 8th to 7th centuries BCE, with significant expansion during the Byzantine era. Extending approximately 60 metres deep, the city could accommodate up to 20,000 people, including livestock and provisions. It features living quarters, communal spaces, stables, storage rooms, and a large meeting hall, all connected by narrow tunnels and passageways. The city's advanced ventilation system ensured fresh air, and an intricate water supply system protected its wells from contamination. Massive circular stone doors, operated from the inside, and concealed passageways provided robust defence mechanisms. Daily life in Derinkuyu included food preparation, wine production, and religious worship, with evidence of kitchens, stone ovens,. Today, Derinkuyu is a major tourist attraction, offering guided tours that showcase its historical significance and the ingenuity of its ancient builders.