The driest non-polar spot on Earth is in Chile's the Atacama Desert where rain has never been recorded yet.
It's hard to overstate just how arid the Atacama, a plateau on the coast of northern Chile, really is. The Andes Mountains work like a 13,000-foot-high wall, completely blocking systems of moist air that might otherwise wander down from the Amazon Basin. As a result, the entire Atacama, a strip of land 1,000 miles wide, is virtually rainless. Arica, one of the desert's largest cities, receives an average annual rainfall of 0.76 millimeters, about the height of a flea egg.
There are weather stations in the Atacama that have never recorded any rain. The town of Calama went without a single drop of rain from 1570 to 1971 more than 400 years! There are river beds that have been dry for 120,000 years, and scientists think that the Atacama has been a desert for over three million years, which would make it the oldest dry spot on Earth.
The waterless Atacama is so unearthly that it's regularly used as a stand-in for Mars, both by Hollywood movie crews and by NASA. Before scientific instruments are launched into space on Mars probes, they perform the same tests in the dusty soil of the Atacama to make sure all systems are go. Other astronomers go to the barren Atacama to watch the skies. ALMA, the world's largest telescope array, opened there in 2013.
Despite the aridity, there are zones in the Atacama where algae, lichens, and cacti grow happily. That's because there's a marine fog called the camanchaca that rolls in from the Pacific Ocean, letting these clever plants pull the moisture they need directly out of the air. Local villagers are catching on, too. Some are now stringing plastic netting to harvest fog water straight out of the air, which they can use to drink or water their gardens.