When ocean explorer and filmmaker Mike deGruy dies unexpectedly in an accident, his wife returns to the edit room to make a film.

Between 250 and 900 CE the Maya civilization perfected mathematics, astronomy, architecture and the calendar. From around 900 CE the Maya's luck ran out and their great cities were largely abandoned. Why?

In 1,200 BCE the Hittite Empire, the Mycenaeans, and the Egyptian Empire imploded and the Bronze Age period of history collapsed. What, or who, was to blame? Evidence points to what is known as the Sea People. Were they responsible?

In 2334 BCE the Akkadians conquered and united the Sumerian city state kingdoms to create the world's first empire. After only 140 years the Akkadian Empire fractured. Why did they collapse?

In 373 BCE the Greek city of Helike disappeared beneath the waves. In myths, Poseidon destroyed it. It's hauntingly similar the story of Atlantis. Could it be possible to rediscover the lost city and could Helike actually be Atlantis?

8000 years ago, a lush paradise, home to mammoth, deer, and hunter-gatherers connected Britain and mainland Europe - Doggerland. It was wiped out by a single devastating event, leaving it hidden beneath the waves of the North Sea.

Sodom stood for 1000s of years as a powerful lesson of the perils of wickedness. According to the Bible, the men of Sodom were so wicked that God destroyed the city in a shower of fire and brimstone. But did the city of Sodom ever exist?

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

This is the final episode of this series.

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.

At Göbekii 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.

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.

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

Episode 7/10 of the Gaia series.

Episode 10/10 of the Gaia series.

Episode 8/10 of the Gaia series.

Episode 9/10 of the Gaia series.

Episode 5/10 of the Gaia series.

Episode 6/10 of the Gaia series.

Episode 3/10 of the Gaia series.

Episode 4/10 of the Gaia series.

Episode 2/10 of the Gaia series.