Ancient Aliens has traveled to many mysterious sites that seem to defy explanation. Now, Giorgio Tsoukalos takes a look back at some of the most incredible structures we've visited all over the world. Structures that, as far as Giorgio is concerned, provide undeniable evidence of extraterrestrial contact.

Ancient Aliens has examined the oldest and most mysterious rock art on Earth–up close and in person. Now, Giorgio Tsoukalos takes a look back at the incredible hieroglyphs, petroglyphs, and geoglyphs that he believes tell a worldwide story–of alien visitation.