Call me a masochist, but I've come to cherish my outings with Julia Solis, a flame-haired original who lives in a rough part of Brooklyn, New York, near the fetid Gowanus Canal. She's smart, amazingly curious and absolutely fearless. These qualities come in handy during her frequent explorations of urban ruins—abandoned aqueducts, tunnels and factories—where light is scarce and mold and spores express their colonial tendencies unchecked. She finds beauty in industrial decay, architectural excesses, cabinets full of old medical equipment, and the steel beams that drip rust into decrepit tunnels.

"These places contain the residue of the many souls that have passed through over the years," she says. "The less a place has been explored, the better, because the air hasn't been diluted and the soul marks are fresh."

On the side, Solis tracks building implosions across the country. The structures to be destroyed are almost always places she would love to explore, and she hates to see them disappear. But she loves to witness their final moments. The only time I've ever seen her angry was when my poor navigational skills caused us to nearly miss an important Philadelphia implosion. We got there just in time, and Solis' face went slack and her eyes got soft as she watched the building drop and the dust cloud rise. Then she scurried off to meet with the explosives teams, seeking information on future spectacles.

The next time we spoke, she was preparing to pilot an inflatable raft through her favorite water tunnel under Manhattan.

"It's the most incredible place I've ever been," she gushed.

Solis is part of a loosely knit tribe of urban explorers, found all over the world, who choose to take on abandoned city locales in much the same way that outdoor enthusiasts try to conquer remote rivers and mountains. Born in Germany, she lived there until high school, when her family moved to Los Angeles. Her European manners and bohemian beauty create a startling effect, and she draws a lot of stares. Now in her late 30s (she declines to reveal her exact age), Solis has made an art out of her passion, documenting her discoveries on her Web site (www.darkpassage.com) and in a series of short stories. She's also organized a group, Ars Subtteranea: The Society for Creative Preservation (www.creativepreservation.org), that strives to increase public awareness of these forgotten spaces through art shows, preservation campaigns and even public treasure hunts.

Last August, a few hours before the great blackout of 2003, I headed north out of New York City with Solis and one of her cohorts, a young spelunker who goes by the name of Cramp. The plan was to explore a subway station and tunnel in Rochester, New York, that had been decommissioned in 1957.

When we reached the exit for Utica, about two-thirds of the way to Rochester, Solis, who wore a giraffe print skirt above clunky black shoes, decided we should find a "respectable steakhouse" to fortify ourselves. I worried that we didn't have time for a leisurely lunch, since we wanted to find the tunnel entrance while the sun was still out, but I was given no choice. When with Solis, you have to trust Solis, and that trust is part of the art of urban exploration. "It's a shared experience," she explained later. "You run around together in an extremely stimulating and often dangerous environment, always on the alert, and you pass out together on a roof somewhere and it's almost as if you're fighting a war together—the bonds formed during explorations can be very tight."

All of a sudden, a little nourishment seemed like a very good idea.

"Head toward the courthouse," Solis instructed as we entered Utica. Years of driving through towns in the Northeast have given her many practical survival skills, and sure enough there was a steakhouse just across the street from the court.

Satiated, we drove on as news of the blackout came over the car radio. We arrived in downtown Rochester to find the stoplights out and the city's police force preoccupied with clearing intersections. "That's good," said Solis, "because they'll be less interested in what we're up to."

At the edge of the Genesee River, we climbed a low wall and dropped onto the abandoned track bed of the cavernous space that was once the Court Street station of the Rochester subway system. The graffiti-covered archways overhead let sunlight into the station. A water main ran across the ceiling, and large leaks released lovely waterfalls onto the concrete, creating a giant pool that reflected dapples of light onto the ceiling.

Flashlight in hand, Solis led us into a narrow passage straight ahead. An eerie sound spooked Cramp and me into hanging back as Solis forged ahead. She soon discovered that the monster in the darkness at the end of the short passage was nothing more than a valve hissing warm steam. "What a cozy spot to pass a cold winter day," she said.

Back in the station a man was sitting on a concrete wall talking to himself. Solis frequently encounters homeless and maladjusted people in her explorations and always treats them with respectful indifference. They are a potential hazard of the trade, but also, like the buildings, they're manifestations of what our culture chooses to abandon and ignore. As we cautiously approached, the man emptied a can of spray paint into a bag, put it over his face and inhaled. He rolled his eyes, oblivious as we passed, green paint marking a sad circle around his mouth.

During our first meeting three years ago in a Brooklyn coffeehouse, Solis gave me a once-over that made me feel like an undercover cop trying to infiltrate a gang. Her hair, as usual, was dyed an unnatural shade of red and she sported a Prada skirt and a shearling coat. Cramp, her principal partner in exploration, was at her side. Thick tribalistic posts disfigured his earlobes and he carried a satchel containing a miner's lamp, rope ladder and other useful equipment.

On our first outing, on a cold, overcast day in the winter of 2001, we drove out to an abandoned mental hospital on Long Island. There Solis led us into the building's old power plant, where the control panel still blinked. Solis searched for meaning in the psychic footprints of the long-gone mental patients—discarded logbooks and other detritus, such as a hangtag for a "Europeanized Hair Wig" collecting dust on the floor and a poster of Martin Luther King Jr. fluttering on a wall.

The photographs she took incessantly she would later use on her Web site. One of the most creative of the dozens devoted to urban exploration, Solis' site bills itself as "providing blind archaeologists with the finest quality flashlights." Solis also holds elaborate participatory events, like the time she took 50 or so neophytes on a haunting walk through dripping darkness, past hibernating bats and strange stalagmites into New York City's abandoned Croton Aqueduct, which was completed in 1842. A mile or so into the tunnel, deep under the Bronx, the crowd was treated to a surprise fireworks show, with rockets spinning along the tunnel's rounded walls. Then a spelunker's ladder was dropped from a manhole in the ceiling, and the walkers climbed up to find themselves on a busy New York City sidewalk. "I'm a conduit for communicating the potential of these dark places to other people," Solis tells me. She first began exploring as a young girl in her native Germany, when she took a group of neighborhood kids into a culvert near her home in Hamburg. But her passion didn't kick into full gear until about ten years ago when she relocated from Los Angeles to New York City, where she now works as a freelance writer and translator.

She's never been married, and isn't, she says, much interested in having children. Her boyfriend is a taciturn graffitist who has painted his autobiography on hundreds of panels scattered throughout the New York City subway system—obviously a match made in heaven.

As we followed the track beds of the dark Rochester subway tunnel, we came to an area that was flooded with golden, late-afternoon light, as though we had just entered a painting by Vermeer. The light came from small openings where the tunnel ceiling met an automobile overpass. Cars passed, chu chunk, chu chunk, over a manhole cover above our heads.

"That's one of my favorite sounds," Solis said, as though it were a lullaby.

A chair sat on a square of plywood on the dirt floor of the tunnel. A real estate flyer, a pornographic magazine and an empty box of antidepressants formed a poignant tableau. Soon, the tunnel ended at a verdant slope leading up to the city streets. We had no idea where we were, and the neighborhood seemed a little rough. A group of kids taunted us and threw rocks as we reentered society. "It's a hazardous profession," Solis said, as we headed for the tall buildings visible across the river.