A look is taken at spaceships powered by A-bombs, fake rings around a star, an incomplete transmission from the moon and lightning that talks to itself.

Experts debate why two suns were photographed in the sky over Indonesia; NASA scientists are baffled by ghostly white swirls on the Moon's surface.

A mysterious object that looks like the Death Star is seen orbiting Saturn; new evidence could shed light on the mysterious death of the first man in space.

Scientists reveal how they're using cutting-edge technology to stop an asteroid catastrophe and how they're closer than ever to being able to keep Earth safe.

Experts believe that despite the planet Mercury's small size, it has a dangerous secret that could one day threaten life on Earth.

Experts explore a 9,000-foot tunnel system that was built into an abandoned quarry by an eccentric millionaire centuries ago for an unknown reason.

A buried ancient city hidden five stories underground is featured as experts use advanced technology to learn more about the strange place.

New discoveries made at the world's biggest underground cave system, which is 1,552 miles long, reveal long-lost secrets of the past.

Treasure hunters attempt to find a long-lost mine that's rumored to be hidden deep inside a remote mountain that holds a precious mineral.

Experts explore a system of underground vaults in Scotland that were once used by thieves to steal and hide recently buried bodies before selling them.

A hidden city built within the Rock of Gibraltar is spotlighted, and experts explain how the immense fortress was used to control the seas during World War II.

A vast system of tunnels build almost three thousand years ago are spotlighted, including how these mazes-like passages were used as a deadly weapon.

Deep in the Balkans, a space-age structure sits dilapidated among the mountain forests of Croatia, so experts work to determine who built it and its purpose.

Dark secrets and a sinister history find a home in a holiday house on the beach of the Black Sea that could have connections with Russia's criminal underbelly.

The remains of the rush to find riches sit in the form of a ghost town in the Colorado mountains where people sought their fortunes from the unforgiving rock.

The chambers of a bunker from a time long past are explored and the remains of the once cutting-edge technology within analyzed to discover its nuclear history.

Experts investigate a giant concrete box on the coast of an island near mainland China, and they discover tunnels that lead to a gigantic underground complex.

Experts investigate a desert island in the Gulf of Mexico that boasts a huge military fortress that was transformed into a prison plagued by deadly disease.