For much of 2005, I walked the same five-block stretch of Rivington Street, on New York City ’s Lower East Side. A direct route to my favorite bars and restaurants, the street was lined with tenements and storefront bodegas that I usually strode right past. Then one day something stopped me in my tracks.It was a painting. Rising up against the dirty white brick of a derelict building, this was no hurriedly sprayed graffiti. It was a beautiful, arrestingly detailed black-and-white image of a young boy in a baggy T-shirt, one arm raised proudly above his head as if to show off his biceps.The portrait was a complete mystery. Who was the boy? Who had painted him, and why here, where he seemed to be growing right out of the sidewalk? Intrigued, I started looking for other great street art on the walls and alleyways of my city—and I found them everywhere.“Street art can change your relationship to a place,” says Marc Schiller, cofounder with his wife, Sara, of WoosterCollective.com , a website devoted to street art around the world. (The duo, well-known street-art aficionados, have lectured on the subject at the Tate Modern in London .) “It opens up your peripheral vision, so you start to notice things you didn’t before. You start to tap into a city’s underbelly, its soul.”If the proliferation of street-art galleries, exhibits, online photo albums, and websites like Streetsy.com and Unurth.com are any indication, people are increasingly enthusiastic about finding that “soul.” These days, says Sara Schiller, people “don’t just make a beeline for the big museums. They walk around and explore…and see what people are putting up without permission.” That could mean poking into mural-covered alleyways in Melbourne and São Paulo , venturing into far-flung, nontouristy neighborhoods around London and Paris , or visiting iconic sites of political unrest, like the West Bank and remnants of the Berlin Wall.Of course, what some call soul, others call vandalism. Even exquisitely crafted street paintings like the one that first grabbed me (which turned out to be the work of Swoon, now an internationally famous street artist), or the stencil paintings of Banksy, which have fetched six-figure prices at Sotheby’s auctions, are illegal in most places around the world. Consequently, the preferred media for many street artists—stickers, posters, stencils, and wheatpastes (drawings that are cut out and slapped up with adhesive, like sheets of wallpaper)—are ones that allow for quick-and-dirty installation.But according to Marc Schiller, street art’s fly-by-night quality—the fact that it can be torn down or obscured just hours after it appears—is part of what makes it magical.“There’s an energy about street art that you know is ephemeral,” he says. “Your relationship with it becomes really immediate and personal, almost visceral. It may not have staying power—but it has power.”