On a busy Friday evening at rush hour, I took a pleasant stroll from the heart of the University of Pennsylvania campus into Center City. I've made the trip hundreds of times before, at all hours of the day, but pleasant is not a word I would have ever used to describe the experience of trekking through that urban Sahara.

Terrifying, perhaps. Oppressive, definitely.

Normally, I would have slogged, like so many students and Penn employees, down Walnut Street, navigating a sequence of dreary railroad viaducts, before joining the stream of refugees marching single-file on the Walnut Street Bridge's narrow sidewalks, as cars whizzed by at interstate speeds. Reaching the Center City side of the Schuylkill always felt like arriving at an oasis of civilization.

But with the completion of improvements by the city and Penn, the way we connect between Philadelphia's downtown and the university has been radically reconfigured. It is now possible to make the trip by navigating a series of peaceful, landscaped spaces. And thanks to a federally funded sidewalk-widening project, the worst stretch - over the Schuylkill - has been transformed into an almost urbane experience.

I began my trip to Center City at Shoemaker Green, the new university park by Philadelphia's Andropogon Associates on 33d Street, in front of the Palestra basketball arena. From there I followed a shady path that hugged the curve of Franklin Field's arched brick facade, toward a picturesque modern footbridge.

As I emerged on the other side, a spectacular panorama opened up, revealing an expanse of emerald playing fields set against the luminous, movie-set backdrop of the city skyline. It was Penn Park, by New York's Michael Van Valkenburgh Associates, one of today's "it" landscape architecture firms. The steel-and-wood bridge provided the kind of perfect, postcard vantage that magically airbrushes cities of their flaws.

From the bridge, I could see a variety of paths rambling through the athletic complex. I chose the circular high road above the baseball field and tennis courts. It swept me around the facilities on a garden-style walkway bordered with tumbling grasses, before depositing me at the newly improved Walnut Street Bridge.

The route was slightly longer than walking straight down Walnut Street, but it provided something that's too rare in cities: the experience of moving through beautiful spaces. This was something planner Edmund Bacon understood when he threaded a pedestrian lane called St. Peter's Way through Society Hill in the 1960s. Walking through Penn's connected parks was like experiencing a larger, more expansive version.

Penn's sequence of spaces is more of an accidental greenway, the by-product of President Amy Gutmann's fund-raising prowess, which has netted the Ivy League school a staggering $4 billion in the last five years.

One of the top items on Penn's to-do list had been to improve its athletic fields. The purchase of a 24-acre surface parking lot along the river enabled the university to create the sprawling Penn Park complex without infringing on West Philadelphia's residential neighborhoods.

Initially, I was not impressed by the $46 million project. Sure, it provided deluxe playing fields for Penn students, but what good was the "park" to the rest of us? Even though Penn allows city residents to schedule games when the fields are not in use, I was hoping for a broader civic benefit. It was particularly disappointing to see a surface parking lot adjacent to Walnut Street. It's the last thing that dull stretch needs.

Shoemaker Green changed the way I saw Penn Park. Instead of gazing at it from the city's bridges, I had an excuse to step inside. Among other things, the little park - 2.75 acres - provides the welcoming entrance that Penn Park lacks.

The site, wedged between the Palestra and Franklin Field, had been previously occupied by tennis courts. To hide them Penn built a wall and earth berm, so people passed the celebrated arena without ever getting a good look at Charles Klauder's handsome 1920s facade.

Once the tennis courts were moved to Penn Park, Andropogon was able to open up views of the surrounding buildings. You've never seen the Palestra this way before. Or Franklin Field. Or Skirkanich Hall, the fine engineering building by Tod Williams and Billie Tsien. Suddenly this disparate collection of academic buildings feels like an ensemble, with the park as the town green.

Unlike Penn Park, Shoemaker Green (named for a trustee) is really a park, where you can lie on the grass or enjoy a coffee from the new Franklin Field cafe. It's sure to become the go-to gathering spot for sporting events at the two arenas, as well as graduation at Franklin Field.

For the rest of us, it will also be a place to wander through. Its 33d Street location makes it especially convenient to the legions who work at the hospital complex, but live in Center City. The park functions as a hinge, linking Penn's other landscaped spaces, like Smith Walk and College Green.

It's a lucky coincidence that the Walnut Street Bridge upgrade is now being completed at the opposite end of the route. From the day the bridge opened in 1991, it was criticized as interstate interloper, a highway inserted into the city. It took the federal stimulus program for the city to secure the $3.2 million necessary to make it fit for pedestrians and bicyclists.

When it's done, probably next week, the sidewalks on both sides will be four feet wider and lined with pedestrian-scale streetlights, instead of highway-style cobra lamps. Cars get two lanes, down from three, and bicyclists will have a buffered lane of their own on the left side. The Schuylkill Development Corp., which oversaw the design, also persuaded PennDot to reduce the size of the interstate signs - a psychological trick intended to get motorists to slow down.

We tend to measure urban progress by each new building the city adds. By the end of my walk, it was clear that the spaces between our buildings do as much to shape our quality of life. They reveal how far we've really traveled.

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