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

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

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

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

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

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

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

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

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.

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.

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

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

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

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

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

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