The ruins of an ancient city in southern Mexico have yielded evidence of long-lost underground tunnels.
Scientists have suggested that subterranean lava tubes on Mars could be home to primitive alien life forms.
The former Fox News host also claimed that there are UFO bases both underground and under the ocean.
Scientists have found a way to reliably tell the difference between a natural earthquake and an underground nuclear explosion.
A road in the UK has become so warped that parts of it are now sitting at a 45-degree angle.
An eagle-eyed Google Earth user has identified what appear to be several underground tunnel entrances.
Many people were left puzzled recently when DARPA made an urgent request for subterranean tunnels.
Evidence of an ancient interconnected subterranean groundwater system has been discovered on Mars.
A new study has revealed that ancient Mars had the right conditions to support subterranean microbes.
Scientists have discovered a superbug that has remained isolated underground for millions of years.
Scientists believe that Mars is now so dry that any life forms would have to be living deep underground.
A peculiar, foul smelling black liquid has been filmed pouring out in to an underground walkway in Japan.
70-year-old Peter Lohr claims to have located five nuclear bombs inside a network of underground caverns.
Subterranean passageways once believed to be an urban legend have actually turned out to be real.
A new species of centipede has been found inside a cave system 4,700ft below the Earth's surface.
A unique ecosystem discovered 1,000ft underground may increase the odds of finding life on other worlds.
A subterranean complex covering an area of 5 million square feet has been unearthed in Nevsehir.
An underground World War II complex used to develop nuclear weapons has been unearthed in Austria.
A massive reservoir of water three times the volume of all the world's oceans lies 700km underground.
A subterranean coal seam fire in Australia has been burning continuously for more than six millennia.