CHICAGO—Of all the face-offs and provocative pairings that enliven the Art Institute of Chicago’s new Modern Wing, perhaps the most striking is the vista, from every floor of Renzo Piano’s elegant 264,000-square-foot addition, of the Frank Gehry band shell in Millennium Park. It’s as if Piano, the current favorite among museum builders, were paying homage to the rising starchitect of the last century. Or perhaps it’s the other way around: In its relatively modest size, the Gehry structure seems to acknowledge Piano’s ascendance as light and grace triumph over Baroque excess. Either way, it’s a neat showdown, even when the windows in the new space are covered with view-muting, floor-to-ceiling white screens during the day.

The addition, which took 10 years to build, at a cost of $294 million, also looks out on a generous slice of the city’s downtown skyline, a reminder that Piano owes much to the steel-framed skyscraper and to two earlier masters whose talents flourished in Chicago: Mies van der Rohe and Frank Lloyd Wright. (There are even plantings of prairie grass in the ground-floor Margot and Thomas Pritzker Garden, perhaps a reminder of the latter’s early style, and the staircase, suspended on slender steel rods, was reportedly inspired by the former’s design for the Arts Club of Chicago.) Sited behind the Institute’s stately Beaux Arts building on Michigan Avenue, the new wing rises three stories and increases the museum’s size to more than a million square feet, making it the second largest art museum in the country, behind New York’s Metropolitan Museum of Art. A 620-foot-long bridge connects Piano’s restrained addition with Millennium Park, across the street, and overhanging the entrance is the most distinctive of the structure’s several green initiatives, a sunshade, dubbed a “flying carpet canopy,” that filters daylight into the upper-level gallery spaces and saves on electricity.

Piano’s previous designs, which include the Pompidou Center in Paris (in collaboration with Richard Rogers) and expanding the Morgan Library in New York, have been praised for relating well to their surroundings. But here, the new building does not seem intended to complement or continue the architectural vocabulary of the original 19th-century museum. Indeed, new and old are sufficiently separated that from the street it is almost impossible to consider them as members of the same family. More than anything, the new structure seems marked by its ability to gracefully combine weightiness and weightlessness. A series of heavy walls made of the same Indiana limestone as the rest of the museum frame the main entry and are lightened by the towering glass-and-steel façade punctuated by slender columns, while from Monroe Street the building has a temple-like assurance, even as the attenuated columns and glass façade project a feeling of weightlessness. Inside the grand central Griffin Court, where the ceiling is three stories high, comparisons can be made to an Italian galleria or a soaring cathedral.

But the real test — as for all art museums — is how well the architecture gets out of the way so that visitors can look at the art. And this the Modern Wing, for the most part, does superbly. The long central hall has already been criticized as an invitation to chaos (admittedly, the Cy Twombly sculpture installed there looks almost lost), but on Saturday, May 16, at the official opening, a generous throng seemed to be navigating that space with no difficulty.

Small complaints aside, the Modern Wing is a wondrous reminder of the importance of art to a great city’s civic life, especially in hard times. If the connection between the museum’s art of the last 100-some years and everything that came before it is physically and psychically a bit of a leap (a spartan new corridor connects the old building to the new), it’s also a reminder that the journey through art history was not without its own brave strides into the new and the uncharted.