Ancient Aliens

Did a biblical patriarch receive instructions from 200 angels high above the earth? Were the ancient Greeks taught how to work metal by a race of fish-people? And might Egypt's most controversial Pharoah have been an extraterrestrial being?

Giorgio Tsoukalos takes a look back at the top 10 reports of encounters with strange and mysterious beasts that have been investigated.

Counting down the top 10 locations around the world that may be hiding alien bases, including a cavern beneath the ice of Antarctica, a lake in China that is a hotspot for UFOs, and a pyramid under the slopes of Mount Denali.

Throughout the world there are mysterious ancient stones shaped into perfect spheres. Many of them show clear evidence of being manmade and some completely defy explanation. Could the mystery of the stone spheres provide clues about humankind's past?