Adah Bakalinsky says there are more than 650 public stairways in San Francisco. She knows because she's climbed them all, except the newest ones. And at age 90, she still climbs them with friends.

"At the spur of the moment we might decide to walk, to check out something interesting about an area. It's a way of being in touch with different parts of the city. Walks are always full of surprises," said Bakalinsky, who has been walking San Francisco's public stairways since arriving there in 1970.

Bakalinsky is impressive not just because she stays active at her age, but because of the energy she puts into finding new nooks and crannies in San Francisco and encouraging others to do the same. She has written two books on walks using public stairways - one for Los Angeles and one for San Francisco.

Americans have gotten accustomed to navigating through urban areas by car, and the Interstates and arterials running around and through our cities may give potential walkers pause.

But there are discoveries to be made on foot - call it urban hiking, urban walking or just going for a stroll. Paths and trails that have been created over the years, and are still being created, are being discovered as portals to urban epiphanies.

Even in car-jammed Los Angeles.

Author and adventurer Dan Koeppel has led thousands on walks over the past eight years - through historic LA, up to landmarks like the Hollywood Sign, and up and down public stairways.

Koeppel says these treks are akin to "urban forensics." Included in some of his tours is a spot beneath a bridge where there's graffiti written by hobos who rode the rails a century ago.

With urban walks, Koeppel says, "You get to know your neighbors, your city and what people are doing. There's something incredibly satisfying about learning something about your neighborhood you didn't know before."

Each May, he leads a 40-mile, two-day trek called the Big Parade, which starts downtown and ends at the Hollywood Sign. Some people walk just a few miles of the Big Parade. Some do the whole walk. One of the featured attractions is a little-known pedestrian pathway along the Pasadena Freeway. It's "a combination of stairs, tunnels, ramps, spirals and walkways that makes you feel as if you're literally standing in the middle of traffic," he says. In fact, you are standing in the middle of traffic - but protected by a caged barrier.

"It is an absolutely intense experience," Koeppel says.

Elsewhere, Atlanta is developing a 22-mile network of multi-use trails. The project is not complete, but walkers, runners and cyclists are already swarming a 2-mile segment of recently finished paved trail.

Houston is developing trails and parks along its bayous.

And planners in other cities are embarking on similar projects, trying to make their towns more attractive.

Some urban walks can seem almost pastoral. On the trails overlooking downtown Portland, Ore., it's easy to forget that you are in city limits. You walk through stands of Douglas fir trees and hardwoods dripping with rainforest moss.

With its miles and miles of trails curling through forests on the West Hills and other areas, verdant Portland is an urban hiker's paradise.

"When we talk to people in the community, the No. 1 thing they want is opportunities to walk - paths and trails," said Mike Abbate, director of Portland Parks and Recreation.

One of the latest Portland efforts is something called the 4T trail, a tour that incorporates light-rail trains, trolleys, forest trails, and even a sky tram that gives spectacular views of downtown and the surrounding countryside. You can take light-rail up into the West Hills, walk a couple of hours through the woods on hiking trails, come back down on the tram, and take a trolley to downtown.

On urban walks, you're apt to see a greater range of people than you would on a trek in the wilderness. Frequenters of Portland's West Hills include hipsters with tight jeans and sneakers, athletes running in high-tech shoes, and gents and ladies wearing clothes you might expect to see at a performance of the Oregon Symphony.

A similar mix can be found on the trails under development in Atlanta. The project, called the Atlanta Beltline, is being developed along an old rail corridor.

"It slices through the city in a way you can't do by car," said Ryan Gravel, an urban planner who came up with the idea for the Beltline in 1999 while working on his master's degree.

The 2-mile segment completed last year, paved and 14-feet wide, is "mobbed with people walking, jogging and biking," he said.

The Atlanta project is similar to one in New York City called the High Line, an elevated park being developed atop a former railroad spur on the west side of Manhattan.

In some cities, once-forgotten public stairways are becoming an integral part of an urban walk. Many were built decades ago, sometimes connecting hilly neighborhoods with trolley lines or with other neighborhoods.

Seattle residents Jake and Cathy Jaramillo wrote a book about the estimated 650 public stairways in their hilly city, and lead tours that focus on them. Their walks range from half a mile to 5 miles. Folks on the tours have discovered obscure public gardens, and spectacular views of Seattle, Lake Washington and distant mountains. Walkers also are rewarded with fresh perspectives on the city's history and architecture.

"You meet people along the way. They tell you stories and what they know. There is a social element as you get immersed in the neighborhoods," said Jake Jaramillo.