One of the world's most dangerous tunnels--Guo Liang tunnel

High up in the Taihang Mountains that cross into Shanxi, Henan, and Hebei provinces, Guoliang Tunnel is dubbed one of the world's most dangerous tunnels.

The tunnel was constructed in the 1970s by 13 local villagers, who dug the tunnel by hand.

Over five years they used 4,000 hammers and 12 tons of steel bars to break through the mountains.

The road through the mountains opened to traffic on May 1, 1977.