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?

"Ancient Aliens" is counting down the world's top 10 mysterious islands, including sites said to be home to giants, remote landmasses that are home to massive megalithic structures, and even islands that disappear into thin air...