This year's implosion of the real estate market brought a distinct and frenetic period of architectural creativity to a decisive close. Now that it's all over, it seems increasingly clear that historians will date the start of this just-concluded era to a September day in 1997 when Frank Gehry's paradigm-shifting Guggenheim Museum opened in Bilbao.

Gehry's shimmering, still-exciting pile-up of sculpted forms in that Spanish rust-belt city rescued architecture from the last smoldering cliches of post-modernism. It also ushered in a whole new set of cliches that the design world is now frantically trying to unload, no doubt at unbelievable sale prices: the architectural one-upmanship among cultural institutions, the fashion for overwrought and underperforming blobs, the rise of the jet-setting "starchitects." So deeply influential was Gehry's museum that the term "Bilbao effect" has seeped into the civilian vocabulary.

There's no point in blaming Gehry, who was only doing something architects rarely get to do, which is to create something original and personal. Yet, because the output of memorable forms has been so relentless in the last decade, it is easy to forget that Bilbao didn't spring fully formed from the creator's brain. It was the product of years of dogged experimentation far from the media glare.

If you want to understand how the 79-year-old Gehry, who spent a chunk of his career designing shopping centers, got from there to Bilbao, head over to the Philadelphia Museum of Art's Perelman Building, where the Collab Gallery is hosting a little show about a private house that the architect never managed to finish.

Given the modest title -

Frank O. Gehry: Design Process and the Lewis House -

you might assume that the exhibition tells us about designing one man's suburban dream house.

Instead, it spans some of the most fertile years of Gehry's career, offering a narrative stroll through a collaboration that incidentally culminated in a design for the most influential building of the decade. (It also led to a slew of prominent commissions, including a major underground expansion for the Art Museum here.) The show's emphasis is rightly placed on the "design process," rather than on finished, eye-candy models, although there are plenty of those, too.

While Gehry never managed to come up with the perfect house design for his client, Cleveland insurance executive Peter B. Lewis, he spent a good 10 years trying, from 1985 to 1995. He obsessively reworked and expanded his ideas, sort of like Philip Seymour Hoffman's character in the film

Synecdoche, New York

. Completing the building became beside the point.

Lewis met Gehry at a lecture in 1985 and immediately invited him to design his house, little knowing what he was getting into. He gamely played - and paid - along, while the architect moved sculptural forms around like pieces on a chessboard. Four complete, and very different, models of Lewis' suburban home are on display, along with Gehry's studies, drawings and videotaped recollections of the project.

As Gehry evolves his signature sculptural style, the house proposals grow in size and ambition. In order to find ways to realize his wildly curving forms, he sought out the software used to design precision jet turbines, and found it could be applied to buildings. For practical reasons, architecture has long favored straight lines and repeating modules; the aerospace programs allowed Gehry to incorporate non-repeating, asymmetrical and anthropomorphic shapes that had been stockpiling in his imagination.

Gehry's menagerie of evocative forms, which he dubs fish, horse octopus and stegosaurus, make frequent appearances in his design models for the Lewis house.

Soon those motifs start to show up in other projects. We see the fish migrate into numerous works, from an Alessi teakettle to a conference room at a Berlin bank.

Gehry certainly didn't lack for other work during those years. He built a much-praised office building in Prague, nicknamed the Fred-and-Ginger building, after the movie dancers. It's not a coincidence that the nipped-waisted cylinder that plays Ginger in the 1996 design also had a supporting role in the Lewis house.

During his Lewis years, we see the hard edges of Gehry's forms softening as he struggles to obtain the feeling of movement and drapery that he admires in medieval paintings. The exhibit indicates an 'aha!' moment when an assistant suggests that he apply wax to harden fabric, and then drop the cloth over his models.

There are times in the course of this show when you can't help wondering whether the Lewis house is just a collection of arbitrary shapes. Is Gehry throwing more into the pot just because he can? When a Gehry design fails, as Seattle's Experimental Music Center did, his biomorphic sculptures can feel like sullen caves.

By the time he and Lewis amicably agree to call it quits in 1995, Gehry is already hard at work on the Guggenheim in Bilbao. All that playing around at the Lewis house is now deployed for a purpose. He uses the menagerie of shapes to evoke the city's shipbuilding past and baroque grandeur.

The Guggenheim and the rest of us owe Lewis a debt of gratitude. He didn't get his house, but for 10 years, the man effectively subsidized the R&D for Bilbao.

Home Show

"Frank O. Gehry: Design Process and the Lewis Hous

e

" is at the Philadelphia Museum of Art's Perelman Building, Fairmount and Pennsylvania Avenues, through April 5.

Hours: Tuesday through Sunday, 10 a.m to 5 p.m. Adults, $7; seniors, $6; children, $5. Information: 215-763-8100 or

.

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