Ancient Astronaut Theorists explore the volcanic lava tubes in Pluto’s Cave, in this clip from Season 18, "Ancient Aliens On Location:...

Documented eyewitness accounts of strange UFO activity at the Solomon Islands has led to a theory that an underwater alien base is...

A strange keyhole-shaped formation protruding from Mars may directly correlate to a similar structure on Earth - Theorists believe...

Plato's account of the lost civilization of Atlantis causes controversy. Still, theorists believe its existence was real, and Atlanteans...