He had not merely found a cave. He had unearthed something far older, far larger, and far more mysterious than he ever could have imagined. Let’s uncover the astonishing truth behind his discovery.

Hidden beneath Turkey's Cappadocia region, Derinkuyu is a vast underground city that once housed 20,000 people and remains a marvel of ancient engineering.

The Paris Catacombs are 65 feet underground. The ancient city of Derinkuyu lies 279 feet below Turkey. The Greenbrier Bunker in W. Virginia is 720 feet underground. It was built to keep Congress ...