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

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

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.

From ancient footprints to mysterious earthworks, Graham continues his journey into the past alongside experts and curious minds, including Keanu Reeves.

Although thousands of miles apart, Graham considers the possible link between the shamanistic use of ayahuasca in the Amazon and tobacco in New Mexico.

At Mexico's Temple of the Sun, Graham experiences the extent of the Mayans' astronomical expertise and investigates their complex calendar system.

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