The Mystery of Nan Madol (S15E01)

Giorgio Tsoukalos and David Childress explore the mysterious chain of manmade islets in Micronesia's Nan Madol. Built from a staggering 250 million tons of volcanic rock, could the local legends be true – that strange visitors floated the massive rocks through the air? And might the site's powerful magnetic anomalies be the result of extraterrestrial technology? (History Channel)