Coober Pedy is located in Australia
Coober Pedy is a town in southern Australia which around 150 million years ago was covered by ocean. When the water receded, the sandy silica minerals from the seabed flowed into the rocky cracks and cavities and solidified over time into the multi-coloured gem-stone, opal. Traditionally it has been a mining town ever since the discovery of opal, but the existing cavernous mines coupled with the intense heat outside made some people take a novel approach to building - going underground.
Submitted by Petro. More information about this location can be found here.