Underground cities seem to be everywhere.
There is an interesting page devoted to them, which features several.
How about the building development
, where, instead of building more suburbs, they are
building down, not up.
Check out this page for
several pictures of undergound
There is a troglodyte village in the Rhone, France:
Derinkuyu Underground City is an ancient
multi-level underground city
of the Median Empire in the Derinkuyu district in Nevşehir Province,
Turkey. Extending to a depth of approximately 60 m, it was large enough
to shelter approximately 20,000 people together with their livestock
and food stores. It is the largest excavated underground city in Turkey
and is one of several underground complexes found across Cappadocia.
There are several interesting underground
towns that survive from the cold war era. There is Norad built beneath
Colorado's Cheyenne Mountain to hold thousands of people in the event
of a nuclear attack. Beijung has a similar installation under the city.
The largest in the UK is the
one under Corsham in Wiltshire.
There is a good BBC
page on this. I won't paraphrase the contents, just click here to have a look.