A Man Knocked Down His Basement Wall, Discovering Ancient Underground City That Housed 20,000 People (Video & Pictures)

Derinkuyu, burrowed more than 280 feet beneath the Central Anatolian region of Cappadocia, is the largest excavated underground city in the world and is believed to connect to more than 200 smaller, separate underground cities that were discovered in recent decades, Turkish guides told the BBC.