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 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, the journalist 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.

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

The author 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.

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

Graham learns of a stone-shaping technique now lost to history, and explores how ancient Amazonians managed to thrive in an inhospitable rainforest.

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

Accompanied by local experts, Graham compares ancient oral traditions and learns Sacsayhuamán in Peru may be older than archaeologists ever imagined.

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

Graham searches for answers to the questions behind ancient works of art, including 25,000-year-old Amazonian paintings and the megaliths of Rapa Nui.