A mysterious American pyramid built out of Cold War paranoia, a haunted prison, and a cluster of structures in the Atlantic are mysterious deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.

Traces of a Russian hole to hell in the Arctic, a military base in America's wild west, and a strange looming tower are mysterious deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.

A secret Russian military base in the Gobi Desert, a strange complex in an American wasteland, and a relic high atop a mountain are mysterious deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.

A secret structure on a sinister mountain, an industrial compound swallowed by a forest, and a mysterious run in a sand dune are strange deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.

A strange alien shrine on a mountain peak, a bridge built in the Alaskan wilderness, and an American castle with a dangerous secret are mysterious deserted engineering projects. New discoveries reveal how they were built and why they were abandoned.

An American ghost town in the Amazon jungle, a secret Nazi base, and a deadly concrete fortress 866 miles long are mysterious deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.

A terrifying sea fortress, a highway in the Amazon that suddenly vanishes, a mysterious structure in the shadow of the Statue of Liberty are deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.