Graham visits Gunung Padang, an Indonesian archeological site, to find proof of a lost civilization — and the potential cataclysm that wiped it out.

In Cholula, Mexico's oldest continuously-inhabited city, Graham inspects the world's largest pyramid for signs of a forgotten past.

Graham discovers a fascinating pattern that may connect the spectacular megalithic temples of Malta, which he believes to be much older than reported.

Few scholars have investigated the Bimini rock formation off the coast of Miami, once fabled to be the road to Atlantis — but Graham dives right in.

At Göbekli Tepe, the oldest known megalith in the world, Graham questions if simple hunter-gatherers alone could have built such an advanced structure.

Graham visits ancient mounds in North America and wonders if they contain astronomical significance — or even warnings of an apocalyptic climate event.

Graham returns to Turkey to explore Derinkuyu, an ancient underground city and survival bunker that could shelter thousands in times of crisis.

In the ancient geological sites of North America, Graham envisions an apocalyptic event that may have changed the Earth — and its inhabitants — forever.