Some, like the Lizard People's tunnel under Los Angeles, promised great treasures, if only you're brave enough to burrow deeply. Others, like the booby-trapped Viet Cong Cu Chi Network, have only death and misadventure for those foolish enough to venture in.
Oobject has a nifty feature of 12 of the most interesting tunnels in the world:
Networks of secret passages and tunnels have been built on a giant scale, from components of the Maginot line to the Viet Cong Cu Chi Network.
Others perform a peacetime function, such as the half mile tunnel network H.G. Dyar built under his Washington home, as a hobby, the passageways under Disney’s Magic Kingdom or the unbelievable 5000 year old Lizard People tunnel network under Los Angeles that the L.A. Times published a diagram of during the depression.
From the Upcoming ueue, submitted by divadwg.
http://underground.cityofember.com/2008/05/japanese-underground-sewer.html