In this episode, Dr. Allan Maca investigates the biggest man-made structure on Earth: the Great Wall of China. This ancient monument has been studied by experts for decades, but it's only now, thanks to new satellite imagery and cutting-edge technology, that its secrets are finally being revealed.

Dr Allan Maca explores the legendary lost city of Xanadu in Inner Mongolia. Today very little remains of Kublai Khan's grand capital - a place that famous explorer, Marco Polo, described as one of the Marvels of the World. But now, with the help of satellite imagery and cutting-edge technology, we can finally uncover Xanadu's secrets, and bring this fabled city and its lavish palaces back to life.

Dr. Allan Maca and his team explore an ancient megacity, the biggest on the planet 4,000 years ago that mysteriously disappeared - a place where the people created Maya-like carvings and humans were sacrificed on an unprecedented scale. Discovering this lost civilization changes everything known about the origins of China, prompting Dr. Allan and his team to solve the mystery.