Arctic Hell Pit

At an infamous prison in the Amazon, the most dangerous criminals on earth faced hard labor, a hostile environment, and death by guillotine; today, it's deserted, and new discoveries reveal why this compound was built and why it was abandoned.

An abandoned town in the Nevada desert are the ruins of an American Atlantis, destroyed by catastrophic floods when the Hoover Dam was built; today, experts investigate the secrets of this ghost town as water levels recede and the city reemerges.

A mysterious castle was once a fairytale estate, but today, the building is said to be haunted, and experts investigate the secrets of this eerie fortress and the ghostly stories inside.

A hidden, subterranean city built within the Rock of Gibraltar was an immense fortress to control the seas during World War II, and new discoveries reveal the secrets of a long-lost chamber with evidence of high-stakes espionage.

A strange, centuries-old labyrinth built into an abandoned quarry was built by an eccentric millionaire, and no one knows why; but now, a new excavation into this mysterious 9,000-foot tunnel system might finally reveal its dark secrets.

A vast system of tunnels built almost three thousand years ago was the site of the greatest battles of antiquity, and these disorienting passages could be the deadliest weapon in war; experts reveal what made this underground world so terrifying.

A mysterious cave system is home to some of the oldest human remains ever discovered, and today, the explorers and researchers investigating this site are uncovering shocking evidence of cannibalism among its Ice Age denizens.

What would happen if we got a message from space? How would we react? Scientists and sci-fi writers, with cooperation from SETI and Carl Sagan's son, Nick, unravel the impact of this world changing event, forming an intriguing hypothetical scenario

How will humans react when an alien spacecraft is on its way to Earth? Will humans learn from aliens, or become colonial subjects? Scientists and sci-fi writers, with cooperation from SETI and Carl Sagan's son, Nick, unravel the impact.

The Arrival has ended. A swarm of small spacecraft depart their huge mothership, and hover in our atmosphere. The ships open their hatches, and deposit thousands of mysterious pods on the earth’s surface. Are they a message, a gift or a weapon?

A mothership the size of Texas is hovering over Earth and we're tired of waiting. We send a rover to explore, and what we find makes us question the definition of life. On Earth, the pods multiply, making contact with them unavoidable.

Astronauts train for weightlessness and fire fighters battle forest fires.

Experts reveal how regular cars are modified to race on dangerous circuits.

The crew of a nuclear submarine reveal how they stay safe during a fire.

Massive mining machines are made to be mobile.

Investigators show how they analyze the data stored on a plane's black box.g