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 ten of the most awesome.
Built in Jordan in the 2nd century by the Nabataeans, this massive monastery is just one of hundreds of dwellings carved into the rocks. Photograph by Martin Gray/National Geographic
2. Barry Troglodyte Village
People have lived for hundreds of years in this village, carved into the rocks of a hillside overlooking Rhone, France.