L.B. Deyo likes to climb the Brooklyn Bridge in the middle of the night. He uses the bright wash of floodlights to see as he hauls himself up the support cables, hanging onto the guide wires of the suspension bridge for dear life until he reaches the top of the towers. The cars below pass oblivious to the spectacle above them: In New York, Deyo says, most people simply never look up.

Solis and Deyo are part of a growing movement of urban explorers, adventurers who go where they are not supposed to be and document their experiences online. Call it "off-limits tourism" or "infiltration." It's not exactly breaking and entering but, rather, visiting boarded-up ruins and underground steam tunnels and the roofs of forbidden buildings. At Solis' Dark Passage webzine or Deyo's Jinx Magazine, and dozens of Web sites such as Infiltration, Urban Explorers Network and Forgotten New York, these explorers are visiting places most of us will never see, and recording it so the future won't forget.

The term "infiltration" encapsulates a whole range of activities ranging from the merely archaeological to the outright dangerous. Climbing through the broken window of an abandoned orphanage may not seem to have much in common with climbing to the top of the Brooklyn Bridge, but the two activities do share a common ideology. "The whole idea is to look at a sign or an area that's obviously off-limits, where you're not supposed to go, and ask, 'What exactly is it that's keeping me out?'" explains Deyo. "We don't break locks or bolts or climb over fences; what we're really overcoming is imaginary barriers that are just understood but barely questioned."

Infiltration is in no way a new concept -- after all, who hasn't clambered through an abandoned building, ducked under a fence to explore or slipped behind a barrier to see what's there? In the '60s and '70s groups like the San Francisco Suicide Club began to codify the modern movement with organized guerrilla adventure groups. But in recent years, thanks in part to the community powers of the Web, the infiltration movement has grown in strength. It's no longer a solitary pursuit; instead, you can join mailing lists, Usenet groups, countless webzines or even the Urban Exploration Web ring to swap tips, scout out good locations and meet fellow explorers. "I don't think there could have been an urban exploration movement as there is now without the Web," says Deyo. "It's a good case study of what the Web can do sociologically; people all over the world send e-mails each and every day. We've even heard from someone who explored a nuclear submarine base in Russia."

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