Below the mountains overlooking Hong Kong’s financial district lies a giant tunnel almost twice the height of a double-decker bus.
Part of a 3.8-billion-dollar drainage network, the tunnel runs nearly the length of Hong Kong Island and has saved the city from floods that decades ago routinely cost lives and caused widespread destruction.
The tunnel intercepts about one third of the rainfall for the northern Hong Kong area, carrying the water all the way to the sea.
Dug with two tunnel-boring machines over five years, beginning in 2007, the 10.5-kilometer-long tunnel protects it from flooding caused by seasonal typhoons.
Hong Kong Island was already criss-crossed by tunnels, including the city’s subway system and roads slicing through the mountains.
The drainage tunnel runs through the hills behind the city, less than a dozen meters below the surface — though few of the city’s residents, whose lives it protects, ever realize it is there.