Guoliang Tunnel Road, China: The Guoliang Tunnel Road, which is carved along the side of and through the Taihang Mountains in Xinxiang, Henan Province, China, has a fascinating history. Construction of the road is said to have been undertaken in the 1970s by 13 villagers from Guoliang, using only chisels and hammers. The project took five years to complete, according to the Daily Mail. Only 12 feet wide, the road offers views of the sheer drop below via 30 tunnel "windows" of varying sizes.