Humans like to build cities that reach for the sky, but sometimes they also build downward. Whether for protection, or just because they can, we’ve created many cities beneath the Earth’s crust – or dug deep into the rocky faces of mountains. Here are nine of the most awesome. via Pocket http://io9.com/9-extraordinary-underground-cities-1492736778
Filed under: My Amazing World Tagged: IFTTT, Pocket
