Forty years ago Robert Venturi and Denise Scott Brown coined the term "decorated shed" to describe a generic building that treated its facade like a billboard. Big-box stores are an example. In their own way, so are more ornate Italian palazzos. The advantage of such open-plan buildings, the pair have always argued, is that they can be easily repurposed for new occupants.

To demonstrate their theory, the Philadelphia architects created their own decorated shed in 1978 at 36th and Market Streets for the Institute for Scientific Information, which pioneered the field of data aggregation. This "dumb box," as Venturi called it, communicated through its facade, a pointillist composition of colored tiles that is often likened to a computer punchcard.

But now their "decorated shed" is generic no more.

Acquired by Drexel University to serve as a new home for its design school, the institute has just been retrofitted by the Minneapolis-based MS&R Design. While they were deferential on the exterior, the architects show just how much room for invention the concept of the decorated shed allows. Behind that placid Market Street facade is one of Philadelphia's most thrilling new designs.

MS&R's designers, Jeffrey Scherer and Garth Rockcastle, didn't merely rearrange the partitions. They exploded them, turning the institute's plain vanilla, open-plan floors into a mind-blowing, Escher-inspired puzzle space. New levels appear out of nowhere. Stairs tumble from odd angles. Natural light streams in. References to a lost past are made visible throughout the building. We could be navigating the retro-futurist world of the movie Brazil.

While MS&R took some liberties with the east facade by adding two large windows, the building's outer casing has otherwise been respected, save for a sign change. ISI is now the Antoinette Westphal College of Media Arts & Design. MS&R even left intact the groovy flower-power panel next to the front door, a Venturi, Scott Brown signature.

The contrast between the calm exterior and the dizzyingly intricate interior could not be more extreme. Some might find the crazy, weaving floor plan disorienting, but it is important to remember that this is no longer a buttoned-down office building. It's a laboratory for design.

The rough industrial aesthetic and free-flowing spaces, in which open classrooms blend into corridors, provide a perfect setting for creativity and collaboration. It's the kind of place that makes you wonder if it's too late to enroll in art school. Course offerings span the digital landscape, from designing video games to architecture.

Scherer and Rockcastle are not new to Philadelphia. In 2007, they created a new corporate headquarters for Urban Outfitters by slipping its fashion design studios into the surviving husks of the Navy Yard's military factories. Their firm specializes in grafting the new onto the old, repurposing buildings without obliterating signs of their previous use.

Urban Outfitters' founder, Richard A. Hayne, made the West Philadelphia project possible by buying the building for $25 million. Drexel, which raised $47.2 million for construction, now refers to the building as the URBN Center.

MS&R began the retrofit by stripping the interior down to its steel bones, revealing terra-cotta-colored I-beams still inscribed with their maker's name: "Lehigh Structural Steel." Then the architects scooped out a big chunk of floor space to create a skylit atrium. Not in the exact center, mind you, but slightly off-kilter. Into this new opening, they inserted a sleek glass elevator and the stairs, made from thick planks of reclaimed maple.

The classrooms, computer labs, studios, and faculty offices revolve around the atrium and are connected by catwalks. The offices and a few specialty labs have permanent walls and doors, but they are made of glass to allow in light. For the most part, student spaces are left open, as extensions of the walkways. They are equipped with tackboard partitions that slide and pivot, so more private, soundproof enclosures can be created when needed.

When I visited recently, no one had bothered to pull the partitions into anything resembling a traditional room. Classes were being conducted in the open, around communal tables. I wandered into a fashion studio while semi-clad models were being fitted. The sense of being inside a buzzing, creative hive was energizing.

The blending of spaces makes for a very densely occupied building. While some square footage was lost for the atrium, MS&R was able to sandwich in an extra floor, bumping up the total from 112,000 to 132,000 square feet. The amount of space for each of the 800 students, 160 square feet, intentionally emulates the standard at creative companies like Google and Microsoft, says Drexel's facilities vice president Robert Francis. This does create some unexpected juxtapositions. You sometimes find yourself at eye level with a floor beam, staring at the feet of some students and the heads of others.

Although the URBN Center's style is very different, MS&R's design shares some of the sensibility of Thom Mayne's new building for the Cooper Union design school in New York. Both were laid out around connecting staircases to foster sociability and collaboration, but MS&R's design is more homey than Mayne's vertiginous atrium.

Despite the spatial complexity at URBN, there are no similar scary moments. Once you form a mental map of the staircases, it doesn't matter that they are not organized in a continuous series.

Most colleges, says Dean Allen Sabinson, tend to be "silo-izers" where students from different disciplines never meet, never mind collaborate. The promise of the URBN Center is that they can begin exchanging ideas just by stepping inside.