Giant Crystal Cave comes to light. Mexico's Cueva de los Cristales (Cave of Crystals) contains some of the world's largest known natural crystals—translucent beams of gypsum as long as 36 feet meters).
The Breakaways near Coober Pedy - Several movies have had scenes filmed here – including one which uses the terrain as the planet Mars. According to the Wikipedia entry for The Breakaways, the average ground temperature can reach 65 degC degF) in summer.
Coober Pedy, Australia: A combination of climactic conditions and the existence of opal mining in the region have literally driven the residents underground. Everything from residences to churches & hotels are carved out of the ground.