''What we do is extremely foolish,'' says L.B. Deyo. ''We don't recommend it to anyone else,'' agrees David ''Lefty'' Leibowitz. ''We urge people not to do it, because it's insane,'' Deyo promises.
What these two 32-year-olds do is prowl New York City's abandoned aqueducts, subway stations, and creaky buildings -- as well as scale its skyscraper-size bridges. (Their uniform? Suits and sunglasses.) The brainy duo, who launched a website and magazine called Jinx devoted to ''urban exploration,'' detail their illegal exploits in Invisible Frontier: Exploring the Tunnels, Ruins, and Rooftops of Hidden New York (Three Rivers, $14.95).
''This is not an extreme sport,'' insists Deyo, a history buff who recoils at comparisons to bungee-jumping Mountain Dew spokesdudes. So what's the draw? ''The intoxicating chance,'' says Leibowitz, ''to see something that no one, or very few people, have seen before.''
Like the entire New York -- New Jersey skyline from atop the 600-foot-tall George Washington Bridge -- which Deyo climbed on Sept. 9, 2001, as Leibowitz kept lookout. ''Your focus is so laserlike up there that you become like a tape recorder, recording every detail in your mind,'' Deyo says.
A planned follow-up -- mounting the TV antenna of the World Trade Center -- was scuttled by fate. ''It would have been incredible if we had been able to pull it off,'' Leibowitz says wistfully. No worries. Their sights are set on a new antenna -- the Empire State Building's.