It's a simple fact of being human, tell us not to do something or go somewhere, and we want it more. And it's these desires that drive today's urban explorers, a group whose main goal is to sneak into and explore abandoned buildings, tunnels, and other man-made structure. As an added thrill, these places are usually hard-to-find, unknown by the general public, and more often than not illegal to venture into. I've done a bit of this type of exploration in some not-so-abandoned train tunnels in New York City, WWII batteries in San Francisco, and forts along the Rhode Island coast. It's definitely an interesting experience, and there's a wealth of information about it on the internet. Check out How Stuff Works' Podcast on Urban Exploration, or the absolutely fantastic show on the History Channel called Cities of the Underworld. And to learn more about the society and the rules that go into this practice (as well as find groups and explorations near you), check out Jinx Magazine, and Urban Explorers Network.