An abandoned airplane hangar in Ukraine was once home to the jewels of the Soviet Union's aeronautics industry, and inside, experts reveal new evidence about its top-secret space shuttle program; these fresh discoveries uncover what really happened here. This episode is a mashup of S06E07 "Towers of Blood" and S06E06 "The Killer in the Castle."

A strange bunker in a treacherous landscape once belonged to a notorious dictator who's paranoid fantasies drove bizarre and elaborate feats of engineering; new discoveries reveal the secrets of these structures and why the nightmares that built them.

The site of strange, alien-like structures hidden deep within a remote forest was once one of the deadliest places in the world, and new evidence reveals who built these bizarre ruins and why. This is a mashup of S06E05 "Florida Doomsday Castle" and S04E09 "Haunting on Plague Island."

An eerie set of buildings in Paris is evidence of an unspeakable evil; new discoveries reveal the horrific things that happened here, and why they were abandoned.

Human bones line a sprawling maze of tunnels beneath the streets of Paris, and this gruesome labyrinth is evidence of a devastating horror; new discoveries reveal the secrets of this strange place and why it was abandoned. This episode is a mashup of S06E04 "Hell on Blood Island" and S04E04 "Labyrinth Of The Dead."

The ruins of an abandoned prison are evidence of a chaotic riot that put the prisoners in charge; special access to its burnt-out interior reveals how inmates took over Ireland's Alcatraz and why it is deserted today.

The ruins of a great wall that once marked the edge of the world hold the secrets of the ancient soldiers who stood watch here long ago; new discoveries reveal who the wall was meant to keep out and why the site is littered with skulls. This episode is a mashup of S06E03 "End Times on Lake Michigan" and S05E02 "American Atlantis."

A massive, alien-like fortress built into a mountainside is the central node to a network of pipelines that race outwards like tentacles; behind-the-scenes access reveals the secrets of why this strange complex was built and why it was abandoned.

Abandoned towers in southern Greece are the ruins of a fearsome warrior civilization descended from the Spartans, and new discoveries reveal the role these towers played during generations of violent blood feuds among the clans that lived here.

An abandoned castle is the site of hundreds of horrific murders perpetrated by the mysterious countess who once lived there. She's alleged to be one of the most prolific killers in history. New discoveries reveal what happened here.

A strange bunker near the Kennedy Space Center once served a top-secret military function should doomsday ever come to the Sunshine State; experts use declassified intel to reveal the sinister purpose of this forbidding facility and why it was abandoned.

An island of dense jungle is home to an abandoned complex with a dark past of bloodshed and rebellion, and new discoveries at this deserted place reveal why it was built and the gruesome circumstances of its downfall.

An abandoned industrial complex by Lake Michigan was once a top-secret military compound that protected America from enemy attacks; new discoveries reveal what really happened here and why the government turned its back on this juggernaut.

In a remote Louisiana swamp, the ruins of a massive industrial operation suggest that something evil once happened here, and new discoveries at this eerie site reveal what these abandoned buildings were for and why they were deserted.

Special access to the world's strangest disaster zones reveals the buried secrets, eerie sightings, and long-lost treasures in ruined, apocalyptic hellscapes; new discoveries reveal why they were built and why they were abandoned.