Ancient Aliens: Extraterrestrial Secrets in Earth’s Depths (S2, E4) | Full Episode

If extraterrestrials influenced human history, can evidence of their existence be found in hidden tunnels and caverns around the world? See more in Season 2, Episode 4, “Underground Aliens.“ Watch your favorite episodes of Ancient Aliens on The HISTORY Channel website at #AncientAliens Subscribe for more from Ancient Aliens and other great The HISTORY Channel shows: Find out more about the show and watch full episodes on our site: Check out exclusive The HISTORY Channel content: History Newsletter - Website - Facebook - Twitter - “Ancient Aliens“ explores the controversial theory that extraterrestrials have visited Earth for millions of years. The HISTORY® Channel, a division of A E Networks, is the premier destination for historical storytelling. From best-in-class documentary events, to a signature slate of industry leading nonfiction series and premium fact-based scripted programming, The HISTORY® Channel serves as the most trustworthy source of informational entertainment in media. The HISTORY® channel has been named the #1 U.S. TV network in buzz for seven consecutive years by YouGov BrandIndex, and a top favorite TV network by Beta Research Corporation. For a deeper dive, visit or follow @history on Instagram, Twitter, Facebook, YouTube and TikTok. For additional press materials visit the A E Networks Press Center at .