A small city of barely 1600 inhabitants, in the desertic region in the central part of south Australia. From when in 1915 at Cooper Pedy has been found the opal, 70 mines have been opened and still today they quarry the precious mineral. But the main feature  of the small town is another one: to escape from the heat wave of the day and from the cold of the night, the inhabitants have built not only underground houses, but also museums, churches and shops. You may stay in an underground motel and you may visit the hypogeous attractions that the mining city offers, including the opal hunt.