When you walk into the small Australian town of Coober Pedy, you may be surprised by what you can see. It's just barren   land there! So why even call it a town? There are more than 4,000 people of 48 nationalities. However, all of the people live underground! Coober Pedy was established  in 1915, following the discovery of opals  . The town is sometimes called the "opal capital of the world," because it is the largest opal mining area in the world. Due to a desert climate  , people came to realize that while working under the ground was easy, living above it was not. The solution was to move underground, by changing old mines into homes and establishing the world's first and most likely, only underground town. As years have gone by, the homes have become bigger. There are now also some hotels for tourists. They come from all over the world just to see this unusual town. Coober Pedy is probably best known for its unique style  of underground living. While the structures  may be located underground, they are in no way worse than those that lie above. Not only do their walls have the color of beautiful red, but also the structures have all the modern equipment like walk-in closets, modern kitchens and televisions. And the town also has gift shops selling opal jewelry, a couple of museums and even a church! Besides, Coober Pedy is also a favourite among filmmakers. And it has appeared in a series of movies such as Pitch Black, Red Planet and Opal Dream. People moved to live underground because  _    .
there were large opal mines there living above the ground was not easy it was the opal capital of the world it was the world's first underground town