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.

Even if you've been to the Catacombs of Paris or have gone spelunking in Brooklyn's abandoned subway lines, there's still a wealth of underground places to be explored. Here are some of the world's less welcoming manmade tunnels and grottos.

The Barry Troglodyte Village is a small complex of homes build undeground in the south of France. Though underground homes are unusual, that's not the weirdest part about this place. These subterranean houses have been occupied continuously by people for thousands of years - from the neolithic era of roving tribes, to …