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You would have to look closely for one of its obscure entrances in the French capital of Paris. But should you stumble upon one, it reveals an underground world of the dark, dank, narrow tunnels with a fascinating history. Below the City of Light's 12million residents lie the remains of 6million others - known as France's Empire of the Dead. The Paris catacombs are a 200-mile network of old caves, tunnels and quarries - and much of it is filled with the skulls and bones of the dead....
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