A strange deserted city in America's heartland, an eerie gigantic wall deep in snowcapped mountains, and a mysterious top-secret Soviet facility are deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.

The world's most mysterious abandoned places are home to dark secrets, and now, new discoveries at these strange sites reveal the untold stories of why they were abandoned. This episode is a mashup of S03E02, "Nightmare on Blood Mountain" and S03E05, "America's Doomsday Town".