The vertigo-inducing Guoliang Tunnel was carved into China's sheer Taihang Mountains by 13 villagers in the 1970s who wanted a link from their remote mountainside village to the outside world. Previously there had been only been a set of steep, narrow and dangerous stairs from Guoliang in the Henan province and it took the men five gruelling years to finish. Uneven and twisty, the single-lane tunnel has various 'windows' where you can peer down the mountain...if you dare.

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