854km (529 miles) NW of Adelaide; 689km (427 miles) S of Alice Springs

People come to this Outback town for one thing: opal. If you're not in Coober Pedy looking for opal, then you're probably here to buy some. And there's lots of it. Coober Pedy is the largest opal-mining town in the world.

On first glance, there doesn't seem to be much here -- but that's because most people live underground. In summer, temperatures can and often do climb to a searing 125°F (50°C), so the locals, well used to digging underground tunnels in their day-to-day work as opal miners, have created a subterranean town -- the biggest in Australia. Underground homes remain at a constantly pleasant 71° to 78°F (22°-26°C). The town got its name from the Aboriginal words kupa piti, commonly thought to mean "white man's burrow."

You can look for opals (called "noodling") on the public noodling reserve in the center of town. Noodling on the mine sites around town is discouraged since visitors have been known to come to grief after falling down the mine shafts.