Sometimes the most familiar-looking works of architecture produce the most radical results. Such is the case with the Salvation Army's Kroc Center, which opened its doors this winter in one of those hollowed-out, industrial-era exclusion zones that pockmark so much of North Philadelphia.

Driving by on a dreary, underpopulated stretch of Wissahickon Avenue, you might not recognize the Kroc Center as a brand-new building; from the road, it appears that ordinary. If you bothered to give the low-slung, sandy-colored brick structure more than a glance, its exact function might not be apparent either. School? Church? Rec center? Social-services agency? The Kroc Center, designed by Philadelphia's MGA Partners, is all the things mentioned above, and yet it is far more than the sum of its parts.

For the hundreds of people who troop in every day to pound the treadmills in the glowing, sun-dappled gym or to swim in the warm waters of the Olympic-size pool, the $72 million Kroc Center is surely the most deluxe new fitness center in Philadelphia. For parents who bring their toddlers to frolic in the children's pool, it is an amenity-laden water park. For the students who arrive every afternoon weighted with backpacks, the 12-acre complex provides the expansive sports fields and computer-equipped tutoring center that their schools lack. And yes, once a week, the Salvation Army holds a Christian worship service in the theater, which is otherwise occupied by music students, community meetings, and arts groups.

It's a little ironic, of course, that profits from the billions served at Mickey D's are what paid for this Big Mac of fitness centers, but so be it. Just before her death in 2003, Joan Kroc, the widow of McDonald's founder Ray Kroc, dropped a check for $1.5 billion into a virtual red kettle so the Salvation Army could build community halls in 27 poor neighborhoods around the country. Philadelphia's center is the ninth to open, and it's got all the fixins imaginable.

When I said the building was familiar-looking, I meant that in the best possible way. Most people won't pay close attention to the exterior architecture, although it is as precise, thoughtful, and generous as any of the fancy college buildings that MGA principal Daniel Kelley has designed for the likes of the University of Pennsylvania and Bryn Mawr College.

The lightbulb moment, when you realize this is not just another make-do, cinder-block, municipal box, occurs when you step into the grand two-story-high lobby, sheathed in glass and pale, anigre wood panels. The space unwinds around a garden plaza like a silk ribbon as it directs members to the training rooms, pools, basketball courts, and yoga studios, all designed in collaboration with Philadelphia's PZS Architects. Because those rooms face the curving glass wall, they receive natural light most of the day, making exercise more pleasure than pain.

Although the Kroc Center is a gift of charity, what makes it special is the conviction that even people of small means deserve the best. There can't be many private fitness clubs - never mind rec centers - that have lobbies furnished with Knoll benches and Platner tables. The pieces are grouped around a gas-fired hearth that encourages people to linger over coffee from the center's cafe.

And people do linger. Not just locals, who are eligible to receive subsidized memberships, but also people who have decent-paying jobs and drive to the center from East Falls, Germantown, and other nearby neighborhoods to produce a polychrome sampling of the city's diversity.

Despite McDonald's contribution to the country's obesity epidemic, Joan Kroc understood how such exercise facilities could transform poor neighborhoods. And because the Salvation Army is committed to healing the soul and the mind, it also included space for drug and alcohol counseling, as well as a small chapel and day care.

The Kroc Center was built in the middle of what used to be the sprawling Budd Co., which manufactured train cars well into the '70s and once employed 10,000 people, operating in three shifts. Those industrial jobs are never coming back, but the placement of the community center in the old factory complex suggests that the neighborhood (Nicetown, now being rebranded as West Hunting Park) just might.

In fact, the best thing about the design isn't the lavish exercise facilities, but the way the Kroc Center has been arranged on the site by MGA and the Manayunk landscape architects at Andropogon. The new building bookends a gutted, but classically muscular, factory loft where Budd sold automotive parts. At the far end, the site is bounded by another industrial-era staple, a long, sawtooth workshop, completing a cozy U-shaped block. SEPTA trains run through the site, alongside the playing fields, and they infuse the ensemble with the promise of urban energy.

While both factory buildings have been empty for years, the Kroc Center's arrival fires the imagination. The loft could easily be converted to apartments, the sawtooth building to studios for artists and fabricators. Similar factory lofts litter North Philadelphia, but too often they're stranded islands. This pair has been pulled back into the living city.

Andropogon has done a wonderful job of integrating the three buildings into the new landscape and making it feel inhabited again. It has layered the site with walking paths that lead up to sports fields and gardens, which have been designed to absorb large quantities of rain and keep it from flowing into city sewers. Sculpted stone runnels, which help channel the water, even create a network of man-made brooks around the site and will surely inspire many children's games.

The Salvation Army project isn't the kind of eye-candy design that makes it into the glossy magazines, or advances architecture, but it just might be the sort that can reshape a neighborhood.