NEW YORK - A taxi pulled up to Apple's Fifth Avenue store one recent morning, and while the meter was running a pair of tourists dashed out to have their photos taken near the entrance, a glass cube of such incorporeal lightness that it seems in danger of floating away.

Had those architectural pilgrims arrived a minute later, they might have noticed a 70-ish man in a rumpled blue blazer struggling to balance an overpacked briefcase on a rolling suitcase. He was hatless, coatless, and tieless, and his shirt pocket was weighed down by a fistful of fine Japanese pencils.

It was the prizewinning Pennsylvania architect Peter Bohlin, stopping by to kick the tires on his little creation, which he first sketched for Apple chairman Steve Jobs using one of his ever-present Itoya pencils. Told that tourists had photographed it with their iPhones, Bohlin chuckled and said, "I hear that happens a lot."

Barely four years after Apple opened the store in the basement of the General Motors tower, Bohlin's ethereal one-story structure - a glorified vestibule, really - has become a must-see attraction as well as Apple's highest-grossing location. According to Cornell University scientists who analyzed 35 million Flickr images, the Cube is the fifth-most-photographed building in New York, the 28th worldwide.

Bohlin has designed many impressive buildings since starting out in Wilkes-Barre 45 years ago, from Seattle's City Hall to Bill Gates' palatial family compound. But nothing has captured the public imagination like the Cube. His work for Apple - including a Philadelphia store scheduled to open in July in a former Walnut Street bank - probably helped him triumph over two superstars, Thom Mayne and Adrian Smith, to win this year's gold medal from the American Institute of Architects, a prize he'll receive in June.

Even so, Bohlin's award was a bit of an upset. The other finalists work on an immense scale. Smith, in fact, just finished the world's tallest skyscraper in Dubai.

Though Bohlin presides over a sizable firm, Bohlin Cywinski Jackson, which has five offices, including one in Philadelphia, he is still best known for turning out rustic-modern country houses that celebrate the power of handcrafted details. He delights in showing off photos of his latest darling: a two-room addition to a Rhode Island farmhouse, a job that required him to design a new water trough for the owners' cows.

His father ran the Faber pencil factory, and Bohlin attended the Cranbrook Academy of Art in Michigan in the late '50s, when it was the intellectual hotbed of American modernism. He now belongs to that dwindling generation of architects who still think by sketching on paper rather than by turning on a laptop.

"He's a total computer illiterate," said his Philadelphia partner Bernard Cywinski, who then conceded, "I am, too, but at least I managed to learn e-mail."

Not Bohlin. He'd rather talk than text. His conversations tend to take place by phone since he has become an architectural nomad, commuting between his home outside Scranton and the firm's offices. It's not unusual to receive several calls a day from him, each from a different city.

"I remember crossing paths with him at an airport," recounted Philadelphia architect James Timberlake. "We sat down and had the most meaningful conversation about architecture. It lasted 45 minutes. That's what clients love about him, I think. He's so deeply engaged."

Clearly, Bohlin's lack of computer savvy wasn't a drawback when Jobs hired him a decade ago to develop a prototype for Apple's foray into the quaint, pre-Web world of street-level retail.

Jobs was concerned that Apple would lose control of its image if it didn't market its personal-computing products through its own stores. Apple is known for its seductively tactile products, and he wanted architecture that reflected that design sensibility.

Jobs, who met Bohlin when the architect was overseeing a new headquarters for his Pixar animation studio, was aware that he had never designed a store interior. But he didn't care about that handicap, said Karl Backus, the principal in BCJ's San Francisco office who manages the firm's Apple projects. That's because Jobs thought of the stores not as retail spaces but as social spaces.

Jobs believed it was more important for the stores to offer a unique and compelling experience, in much the way that a Frank Gehry-designed museum does. Otherwise, why would people bother to make a special trip to buy a product they could order more easily on the Web?

Maybe because he's so sociable, Bohlin uses architecture to make people comfortable in their surroundings. Some of his most successful designs, such as the Girl Scouts Shelly Ridge Service Center, near Ridge Avenue just outside Philadelphia, effortlessly combine simple forms, abundant light, and small details into spaces that feel just right. Inevitable is the word Bohlin uses.

During his first meeting with Jobs to discuss the Apple Cube, Jobs talked about a store that would serve as a sort of clubhouse for Apple's loyal followers. While Jobs spoke, Bohlin drew the rough outlines of a cube in front of the General Motors tower.

"The best thing about that building is its narrow profile. So I thought, 'What is the inevitable shape to contrast that?' " Bohlin said.

The aboveground entrance was only a small piece of a bigger puzzle, however. The retail space Apple had leased below the tower's plaza had been famously unsuccessful, despite its prime location at 59th Street.

"How do you motivate people to come down into a space like this?" Bohlin wondered. The answer was to make the cube into a giant skylight. "There has always been something magical about a glass building," he said.

The arrangement, said Cywinski, created a "ceremony of descent." Instead of being put off by entering a basement store, people feel ennobled, as though making an entrance into a grand house. The sleek glass container becomes "both symbol and portal."

People now flutter around the Cube like moths, as though unable to resist a mirage. The 32-foot-high vestibule contains a round glass elevator wrapped by a spiral staircase, also entirely made of glass and twinkling like an ice sculpture. Customers will line up just to shoot down one flight in a glass cylinder.

It's Bohlin's belief that a well-designed building will "enable people to discover things" about themselves and their desires. "The architecture creates a kind of choreography."

As Bohlin spoke, he was surveying the Fifth Avenue store's sun-dappled, underground showroom. Dozens of customers appeared to be hanging out rather than shopping, just as Jobs predicted. Some tapped out e-mail on display computers laid out like dinner-party settings on the blond, farmhouse-style tables Bohlin designed in a rustic contrast to Apple's smooth, high-tech gadgetry. A group gathered at a corner table for a seminar on video editing delivered by a headset-wearing Apple specialist. The store is open 24 hours; it's just as busy at 2 a.m. as at 11 a.m.

Bohlin worked on the Cube when architectural glass was rapidly becoming stronger and more transparent. BCJ's architects came up with the idea of using multi-ply glass for the wall fins to make them capable of supporting the facade. The only metal in the structure is the stainless-steel bolts that tie the glass panels together. They virtually disappear in the general shimmer.

The Philadelphia store won't be a signature design like the Cube, but it will incorporate key elements of the BCJ prototype, from the minimal scrim of the glass facade to the strict linear arrangement of the tables and products. A second-floor seminar room should help make it a gathering place.

Since BCJ completed the Cube, glass panels have become even stronger. In November, Bohlin and the firm opened a stand-alone Apple store at 67th Street and Broadway that turns the idea of the Cube inside-out, even while offering a paean to glass.

On a trapezoid site, the store is flanked on three sides by 60-foot-high, solid walls lined in a pale Tennessee marble that Jobs selected. But this is also no dark, confined space: The roof is a gently curved glass vault supported by impossibly thin metal beams. Because of the soaring height and transparency, it's as bright as outdoors. Bohlin modestly described the design as a "market hall" - full of Apples - but it could also be considered a minimalist update on the venerable reading room at New York's 42d Street public library.

It's ironic that Bohlin has become a master of glass, because he spent much of his career working in wood. His early houses, including the celebrated "Green house" built for his parents in the Connecticut countryside, were inspired by wooden cabins and often used tree trunks as columns and beams. Those designs also tended to disappear into the surroundings, just like Apple's Cube.

Bohlin sees his Apple work as part of a continuum, a lifetime interest in getting at the essence of architecture. For other architects, Bohlin's work is a corrective to a period of excess.

"People are tiring of spectacle," argued Cywinski.

His buildings aren't "some Cool Whip dropped on the site," added Timberlake. "They're a return to elemental geometry."

Once, highbrow cultural buildings were the architectural trendsetters. But the broad appeal of Bohlin's Apple designs suggests that our common retail spaces may be what set the design agenda in the future.

Contact architecture critic Inga Saffron at 215-854-2213 or isaffron@phillynews.com.