Meandering the streets of a new city is a great way to feel its pulse, but have you ever considered what's right below your feet? These thirteen underground, man-made attractions, scattered around the globe, boast spectacular histories as former dwellings, burial grounds, and even smugglers' tunnels. And you can bet they're more than a little creepy. You'll want to make sure you dress warmly for all of them (no matter when you visit), and be sure to arrive armed with a steely constitution.
By Amanda Oppold