Each started out with the aim of concentrating Philadelphia's cultural power in one part of the city. And after that imperial ambition was thwarted, each remained militantly opposed to allowing displays of commerce to interrupt its vision of grandeur. For years, it was nearly impossible to buy so much as a bottle of water as you slogged between widely spaced monuments.

Given such a legacy, the appearance this summer of two gracious pavilions devoted to the gentle art of drinking coffee and wasting time suggests that the city is getting over its resistance to trade among the trees. If these cafes could ever secure liquor licenses, we'd raise a toast to Philadelphia's growing interest in civic relaxation.

The new cafes, like their respective settings, employ similar design strategies, although they resolve them very differently. Their architects envisioned their pavilions as gossamer porches for public lounging. The see-through structures will offer refuge from the urban bustle, light lunches, and chances to check your e-mail. In a less cautious time and place, the designers might have allowed themselves license to create whimsical garden follies, but instead made sure their constructions blended into the background.

The first pavilion to open is the new Independence Al Fresco Cafe on the mall, a floaty steel-and-glass shelter by Erdy McHenry Architecture. Though the smallest project on the renovated mall, it's easily the most satisfying design. It's also the only one that conforms to Laurie C. Olin's 1998 master plan, which called for an array of diaphanous structures dissolving into the landscape.

What makes the design such a wondrous accomplishment is that it contains not a single red brick or reference to Ye Olde Philadelphia. The architecture is as fresh as the cafe's name, with a modern sensibility that restores the buoyant, hopeful spirit of Mitchell/Giurgola's lost Liberty Bell Pavilion to the mall.

Erdy McHenry was a daring choice for Independence Visitor Center, which commissioned the seasonal shelter, located directly across the mall lawn from its own building. The firm is known for its stylish, but often enormous, residential buildings, so it's interesting to see its sensibility applied on a Lilliputian scale.

The design team - Scott Erdy, David McHenry and Michael Brahler - crafted the $850,000 pavilion with the tolerances of a fine yacht, packing all the necessities of a cafe within the span of a 28-footer. Because the open-air structure pushes several feet beyond the plane of the mall's eastern wall, stepping inside feels like boarding a ship for a sail down Fifth Street.

You get a lovely tableside view of Christ Church's graveyard, carefully stage-managed to edit out the garage ramps below the cafe. Use of white oak for the floors, Eastern hemlock (Pennsylvania's state tree) for the walls, and a circular skylight further accentuates the nautical.

At night, when etched-glass panels are lined up to seal the building, they spell C-A-F-E - an irony that won't be lost on those who recall Venturi Scott Brown's early scheme for the mall, rejected for utilizing the forbidden tools of commercial architecture. That Erdy McHenry could get away with that bold graphic touch suggests Philadelphia's design sensibilities really must be maturing.

Like many recent Erdy McHenry buildings, the cafe is longer than it is tall, but on a shipping-container scale. While eschewing the mall's trademark red brick, the architects kept to the color scheme by cladding the exterior in Cor-Ten steel - the material used for Claes Oldenburg's The Clothespin - because it develops an earthy red coating of protective rust.

A thick outline of the rich, dark steel frames the rectangular cafe, just as the structure itself acts as a frame for the burial ground on one side, the mall on the other. Tables spill out into a garden, but it's a rather lazily designed landscape. The taut cafe structure would have been better served by more plantings with a stronger form, such as boxwood or a tall hedge.

In any case, it might be preferable to sit along Fifth Street, to avoid gazing at the ungainly visitor center, which looks increasingly like a suburban high school, especially now that its planting beds are overrun with weeds. It's a sorry sight for a national park.

Like the Al Fresco cafe, Cope Linder Architects' design for Cafe Cret, now under construction at 16th Street and the Parkway, can trace its roots to Laurie Olin's work at New York's Bryant Park. The Philadelphia landscape architect rescued that derelict public space in the late 1980s, when he reinterpreted its neoclassical plan and installed food kiosks around the perimeter that were designed in a Gilded Age style.

Paul Levy of the Center City District has applied the Bryant Park model to the Parkway, gradually improving the fixtures, crosswalks and its many small park spaces. After 3 Parkway was renovated, its owners offered $1 million to rescue the triangular island on their doorstep, which, like Bryant Park, had become a derelicts' hangout.

For the $1.4 million construction project, Cope Linder's Robert F. Keppel took his design cues directly from Bryant Park. The cafe's vaguely Victorian hip roof will be green, to match the streetlights and blend in with the site's shady London plane trees. Because the walls will be folding-glass panels, the structure will almost vanish when the windows are open. A broad brick-and-concrete apron will enable the cafe to seat 90 and offer a straight-on view of City Hall's tower.

Cafe Cret (named for Parkway designer Paul Cret) isn't as daring as the Erdy McHenry design, but given its location at the entrance to the Parkway, it's likely to be a big draw when it opens in September. Philadelphians have been waiting a long time for a quiet place to relax on their Parkway.

Changing Skyline: If You Go

Independence Al Fresco Cafe is currently open from 11 a.m. to 5 p.m. daily, but hours may be extended as the summer progresses. The cafe is located on the middle block of Independence Mall, along the Fifth Street edge between Market and Arch Streets.