In the Australian desert mining town of Coober Pedy, many people escaped the heat by building into hillsides. According to Wikipedia,
The harsh summer desert temperatures mean that many residents prefer to live in caves bored into the hillsides ("dugouts"). A standard three-bedroom cave home with lounge, kitchen, and bathroom can be excavated out of the rock in the hillside for a similar price to building a house on the surface. However, dugouts remain at a constant temperature, while surface buildings need air-conditioning, especially during the summer months, when temperatures often exceed 40 degrees Celsius (104 degrees Fahrenheit).
They also have an underground church and jewellery stores. Sort of Hobbiton goes to Oz.