Most residents of this South Australian town live underground, to escape the blazing outback heat. There are subterranean shops, a hotel and a restaurant.
Coober Pedy, South Australia —
Most residents of this South Australian town live underground, to escape the blazing outback heat. There are subterranean shops, a hotel and a restaurant.
Satc Milton Wordley
A chapel and cathedral carved out by miners are highlights here, under chandeliers made from rock salt.
Wieliczka salt mine, Krakow, Poland —
A chapel and cathedral carved out by miners are highlights here, under chandeliers made from rock salt.
wieliczka salt mine
Tours pass by neat stacks of bones, including many Parisians who fell victim to the guillotine.
The Paris Catacombs, France —
Tours pass by neat stacks of bones, including many Parisians who fell victim to the guillotine.
Philippe Ladet
Carving of Cappadocia's vast underground cities may have begun three millennia ago.
Cappadocia, Turkey —
Carving of Cappadocia's vast underground cities may have begun three millennia ago.
TINAZAy getty
This former plague-struck part of the city was long sealed up.
Mary King's Close, Edinburgh, Scotland —
This former plague-struck part of the city was long sealed up.
VisitScotland.
When fire swept through Seattle in 1889, another city was simply built on top.
Seattle Underground, Seattle, Washington, U.S. —
When fire swept through Seattle in 1889, another city was simply built on top.
Jeremy Reed
Tours of this engineering marvel, built to keep Tokyo dry during the rainy season, take place three times a day.
G-Can flood surge tunnels, Tokyo, Japan —
Tours of this engineering marvel, built to keep Tokyo dry during the rainy season, take place three times a day.
insidejapantours.com
These underground passages wind from numerous bars and hotels to the river.
Shanghai Tunnels, Portland, U.S. —
These underground passages wind from numerous bars and hotels to the river.
Portlandwalkingtours.com
Come a nuclear war, here's where Congress would have hung out.
Greenbrier Bunker, West Virginia, U.S. —
Come a nuclear war, here's where Congress would have hung out.
the greenbier
You can explore this Viet Cong supply route -- if you're thin enough.
Cu Chi tunnels, Vietnam —
You can explore this Viet Cong supply route -- if you're thin enough.
tamara hinson
Entire immigrant families hid here from persecution, then Al Capone supposedly used the tunnels for smuggling.
Moose Jaw, Saskatchewan, Canada —
Entire immigrant families hid here from persecution, then Al Capone supposedly used the tunnels for smuggling.
Chicago Connection Tour
Nottingham's medieval housing estate has an unlikely entrance -- in a shopping center.
City of Caves, Nottingham, UK —
Nottingham's medieval housing estate has an unlikely entrance -- in a shopping center.
VisitEngland