Coober Pedy is an Australian mining town with such an extensive labyrinth of depleted opal mines that half the town's residents live underground. There are bookstores, churches, and other public spaces.
Since its founding 100 years ago after a teenager discovered opal gemstones there, the town has been ground zero for opal mining. An estimated 70 percent of the world's opal production can be linked back to the town, earning it the title of Opal Capital of the World, and the majority of its 3,500 residents work in the opal industry. One of the latest finds was a set of opalized pearls dating back more than 65 million years—but the city offers other kinds of buried treasure, too. Rather than move to a cooler locale, the town's earliest residents learned to adapt to the hellish environment. They found inspiration on the very ground they stood on: Using mining tools, hardy prospectors did what they did best and dug holes into the hillsides to make underground dwellings or "dugouts." Today about half of the population lives in dugouts where the temperature stays at a constant 75 degrees year round.
Bonus video: Behind the scenes of Mad Max: Beyond Thunderdome, filmed in Coober Pedy.