S7E1: Aliens and Stargates

Legends from around the world speak of sacred entryways to the land of the gods. Gates that allowed instant passage not just beyond the confines of Earth, but beyond space and time. Are such passages--or stargates--just inventions of myth, or might this kind of interstellar travel have existed in the ancient world? In Turkey, researchers uncover a mysterious and toxic cave that the ancient Greeks described as a physical gateway to Hell. The Incas believed their empire began when divine beings stepped through portals in a mountain. In Northern Mexico, legends describe strange, otherworldly creatures appearing and disappearing within the remote ruins of an ancient civilization. As science continues its quest to create technology that would allow humans to travel to the stars, is it possible that these celestial pathways already exist?