Behind the presidential faces of Mount Rushmore lies concealed secrets and the Statue of Liberty contains a dark, enigmatic history; experts use the latest science and technology to investigate and reveal undiscovered mysteries of American monuments. This is a mashup of S03E04 "Statue of Liberty: The New Secrets" and S06E04 "Mount Rushmore: The Hidden Secrets."

The legendary metropolis of Xanadu (Kublai Khan's capital of the Mongol Empire in the 13th century) and its fabled existence have mystified experts for centuries; now, archaeologists use cutting-edge aerial imaging to investigate new discoveries and reveal the truth behind this mythical lost city.