Terrifying encounters at 40,000 feet. Pilot accounts of UFOs taking control of their aircraft. Entire jumbo jets disappearing into thin air. Since the dawn of aviation, pilots have experienced unexplainable events in the sky. Could they have witnessed aliens in our airspace?

Ancient Aliens is counting down the world's top 10 pyramid sites, from a valley in Peru with over 250 hidden pyramids to an ancient Greek city with mysterious 4,800-year-old ruins to Egypt's famous Giza Plateau... Could the extraordinary structures that stand at these sites provide evidence of extraterrestrial visitation?