Experts Investigate a mysterious formation in the Antartic ice.

Experts investigate mysterious formations on a Mediteranian Island.

New data from NASA satellites reveal a sunken lost continent in the Indian Ocean.

A forbidden island points to a strange South American town that locals claim was the home of Adolf Hitler.

Experts investigate an eye shaped lake containing a mysterious floating island.

Experts question the purpose of an artificially created island constructed by the military.

A deadly plague eats away at a Rhode Island forest.

At the height of the cold war, the CIA is confounded by a powerful new weapon dubbed the Caspian Sea Monster.

An eerie green vortex of death swirls in the Baltic sea.

Experts investigate a river surrounded by death.

Experts investigate a seemingly alien lake, that may reveal secrets about Martian life.

A lightning bolt scars the Australian outback.

A ghost ship appears on a California beach.

The search for Nazi treasure leads to a secret underground bunker.

A military satellite witnesses the disappearance of a Russian airliner over an ISIS danger zone.

Investigators uncover an ancient forge from the dark ages.

A military satellite witnesses the disappearance of a Russian airliner over an ISIS danger zone.

Investigators uncover an ancient forge from the dark ages.

This romantic road carved into a sheer rock face in the Rhone Valley in France was an engineering marvel that was once a wild success. What caused it to be abandoned today?

Built in the 1940’s the Goat Canyon Trestle Bridge was the tallest wooden railway system in the world.

Two miles inside a mountain in Croatia lies the remains of a massive, secret Cold War airbase built to withstand a nuclear war.

Now abandoned, this machine once could scan thousands of kilometers.

Explore the mystery behind why a huge gun was built and abandoned.

Hidden in woods outside Moscow is a Cold War weapon that harnessed electricity into a thunderbolt, designed to protect the city.

In the east China sea, there is an abandoned piece of land. Check out why this island represents one of the greatest engineering achievements of the 20th century.

Located in California, Plank Road is one of the most extraordinary engineering achievements of the early 20th century.

Philip Grossman finds firefighting gear under a hospital in Chernobyl, sending his Geiger counter climbing. He believes burying the gear was the Soviet’s attempt to hide the scope of the disaster.

Philip Grossman goes inside the plant near the massive radio tower he finds maps of the U.S and pictures of mushroom clouds. Was the Duga for protecting Chernobyl from incoming missiles or part of a nuclear offensive?

Survivors who worked at nearby factory report production areas they weren’t allowed to visit. Philip visits and finds the basement full of lab after lab of gas masks, radioactive testing materials and sand.

What would receiving a message from an alien civilization tell us about human evolution, and about surviving the most serious problems facing our planet?

Author Nick Sagan hasn't seen his godfather, Frank Drake, in over 30 years. We capture their reunion - and find out how Drake became friends with Nick's famous father, Carl Sagan, in this exclusive clip.

Since the 1960s, NASA has been keeping an eye on man-made objects in space. Here, engineers are replicating the devastating impact of space debris. 'Alien Encounters' airs Tuesdays at 10/9c.