Desolate structures left in ghostly ruins are scattered across the US, and each holds a story waiting to be discovered; experts use cutting-edge tech to investigate these forgotten places and reveal how they were built and why they were abandoned. The segments of this special come from various episodes. 

Tunnels filled with human bones beneath the streets of Paris and ruins of a massive industrial operation contain a haunting past; experts investigate the evil secrets behind these deserted places to uncover how they were built and why they were abandoned. This is a mashup of S06E02 "Swamp of Despair," S04E04 "Labyrinth of the Dead," and S07E02 "American Ghost Park."