Most UFO theories reach for outer space. The cryptoterrestrial hypothesis reaches down instead: it proposes that flying saucers come not from distant planets but from an advanced, hidden civilization that has been living on Earth all along — under the oceans, inside mountains, or beneath our feet.
The idea has deep roots in pulp and the occult, from H.G. Wells's underground Morlocks to a 1940s magazine craze around a man who claimed to be in radio contact with subterranean beings. (His editor later revealed he had spent eight years in a mental institution.) The writer Mac Tonnies gave the idea its name in the 2000s. Even sympathizers keep it at arm's length; one scholar of conspiracy theories calls the whole thing "really more of a thought experiment designed to raise questions."
It has not gone away, either. In the 2025 documentary The Age of Disclosure, the UFO-disclosure advocate Luis Elizondo floats the cryptoterrestrial hypothesis as one way to read the government's own unexplained sightings.
Previously:
• The Pentagon has made more UFO revelations
• 'Flying Saucers are Real!' is an awesome book about UFO culture and history
