The Chapel in the underground city of Naours (France). The comparison to Cu Chi, the tunnels in Vietnam dug by the the Viet Cong in the 1960s, didn't occur to me until later. But the differences are many: this is hundreds of years old, through solid rock, easily built large enough to accommodate even men of my height (188cm), and it's immense. The French Army used it in the First World War, the Germans used it as a supply dump in the Second World War.

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Photo © 2014, Giles Orr

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