Watch Cities of the Underworld online: Episode 7 London's Lost Cities

London, England is Europe's largest city, and for thousands of years, has been among the most powerful cities in the world. Pieces of history can be found throughout London's busy streets and marketplaces. But there's another city hiding below the surface - Roman baths, secret crypts, lost rivers and indestructible bunkers that could hold 8000 people - virtual underground cities. Join host Eric Geller as he discovers the subterranean secrets found below London's most famous landmarks and even finds Winston Churchill's hidden war rooms. We're peeling back the layers of time on Cities of the Underworld: London's Lost Cities.

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