A haunted lighthouse on Lake Michigan, a town where everyone seems to have vanished all at once, and a secret complex of tunnels beneath London are deserted engineering projects, and new discoveries reveal how they were built and why they were abandoned.

A Nazi fortress that could have changed history if it was finished, an underwater graveyard of unexpected American treasures, and a network of tunnels hiding a secret history of New York were abandoned for mysterious reasons, and experts investigate why.