Who says all the beauty is in nature? City dwellers who can't steal away for a real wilderness jaunt can still partake of extreme outings right in their own back yards. It's called urban exploration, or urbex for short, and it's attracting a growing cult following. The idea is to plumb the recesses of hidden and forgotten places in the built environment — everything from under-city catacombs, sewers and transit tunnels to above-ground relics like abandoned buildings and even ghosts towns. Besides thrill-junkies seeking a creepy romp among the ruins or the adrenaline surge of infiltrating prohibited places, many urbexers are also photographers and videographers with an astute eye for the surreal beauty of decayed and dying spaces.