New York is in the cultural doldrums. The city is bursting with gorgeous art exhibitions, but where is the raw energy? Where is the new blood, intent on upending the establishment? Today, once-rebellious talents often seem to be wandering lost in the constellation of celebrity, where they soon settle into complacency.Designed by the Japanese firm Sanaa, the New Museum of Contemporary Art, on the Bowery at Prince Street on the Lower East Side, is the kind of building that renews your faith in New York as a place where culture is lived, not just bought and sold.The architects, Kazuyo Sejima and Ryue Nishizawa, conceived the building as a series of mismatched galleries precariously stacked one atop the other. It succeeds on a spectacular range of levels: as a hypnotic urban object, as a subtle critique of the art world and as a refreshingly unpretentious place to view art.But what elevates the building itself to art is the way it captures an unnerving moment in the city’s cultural history with near-perfect pitch. Its ethereal forms hover somewhere between the legacy of a fading bohemian downtown and the ravenous appetites of a society awash in new money. That the building is so artfully rooted in the present means that its haunting quality will probably deepen as the city ages around it.Ms. Sejima and Mr. Nishizawa may have seemed unlikely candidates to shake up the establishment. The pair is known for work of a high level of refinement and an almost aching sensitivity to a project’s social and physical context. Their most celebrated project, the 21st Century Museum of Contemporary Art in Kanazawa, Japan, is a collection of discrete pavilions enveloped in a glistening one-story glass cylinder — a heavenly village of art whose intricate network of corridors obliterates the conventional museum narrative. Its sleek forms are pieced together with a precision and care that are closer in spirit to the layout of a computer’s circuit board than to the big industrial machines fetishized by the early Modernists.But the architects decided that aiming for a similar level of refinement at the New Museum would have been unwise. For one thing, the quality of craftsmanship in New York is known to be substandard, compared with the workmanship at construction sites in, say, Japan. And the 60,000-square-foot New Museum building was built on a relatively modest budget of $50 million.More important, the museum was intent on staying tethered to what was left of the rough-and-tumble downtown art scene. The decision to move the institution from SoHo to the Bowery was an effort to tap into its history — its uninhibited characters, seedy settings, voyeuristic attractions and, above all, rejection of bourgeois tastes.The seven-story building stands amid the remnants of this forgotten landscape and a new one. The dirty brick facades of a few restaurant-supply stores and S.R.O.’s flank it on two sides. SoHo’s glitzy boutiques and showrooms are a few blocks to the west; the cheap, pretentious glass towers that embody the latest wave of gentrification are rising to the east and north.The museum serves as a hinge between these two worlds. As it rises, its floors shift back and forth like a pile of boxes stacked ever so carefully. Its protective armor of shimmering aluminum mesh is a great ornamental screen. Exquisitely detailed, it is backed by a second layer of metal panels, giving the surface a subtle depth.What results is a striking expression of the neighborhood’s warring identities. When the building is approached from Prince Street, the contrast between the instability of the forms and the uniformity of the aluminum gives it a strangely enigmatic glow, evoking both a fading past and a phantom future. As you get closer, the skin becomes tougher and more industrial, echoing what’s left of the neighborhood’s grittier history.The formal ambiguity is coupled with a fierce desire to bridge the divide between art and everyday life. Only a thin sheet of floor-to-ceiling glass separates the sidewalk from the museum’s ground floor. Inside a lobby and loading dock are set side by side, so that pedestrians can watch the art being moved in and out of the building or gaze across to a small cafe and gallery at the rear of the lobby.From here, visitors can contemplate the chaos of the city in relative silence, forging a seamless connection to the public life of the street. (That seamlessness drives home a practical point, too, since the entire ground floor is open to the public, free.)It’s only when you ascend to the upper floors, however, that you begin to glean the meaning of the museum’s unusual form. By shifting the positions of the various floors, the architects were able to create narrow skylights along the outer edges of the galleries, allowing a soft, diffuse sunlight to wash down their white walls during the day. Rows of fluorescent lights are suspended from the ceilings, and the mix of artificial and natural light gives the spaces a lovely warmth that shifts ever so slightly with the weather or time of day.This talent for extracting meaning from simple but unexpected choices — like shifting the position of a floor or the texture of a material — is what imbues Sanaa’s architecture with a hint of mystery. Here, that effect surfaces in myriad ways. Because the position of the skylights varies from floor to floor, the quality of the light is never exactly the same. Some gallery floors are compact, some tall, and others far bigger but with lower ceilings. They have an intuitive relationship to one another without becoming repetitive.Most significantly, the design brings the art to life. To focus attention on its new building, the museum chose to open with a show of contemporary sculpture; the walls are left entirely bare. Even so, you can feel the architects’ empathy for the artist’s hand. The gentle shifts in scale, proportion and light heighten your awareness of the surroundings, which, in turn, draws you closer to the artworks. The shifting mood of the rooms constantly encourages you to observe the sculptures from different, unexpected perspectives.That effect is reinforced by the rawness of the spaces — exposed beams, painted white walls, cracked concrete floors. The informal quality makes the art feel wonderfully accessible. There is nothing ostentatious here, none of the fussy detailing or fancy materials that create an invisible barrier between viewer and art in so many contemporary museums and galleries.There are other surprises. A narrow staircase, 50 feet long and 4 feet wide, connects the third and fourth floors, exaggerating the distance between the two and heightening your anticipation to the point of torture. At the top, a narrow wedge of space connects the staircase to the gallery, inducing a sudden sense of compression before you experience the release of stepping into the exhibition. Elsewhere, a few eccentric pockets of space are set in the corners for more intimate installations.It will take some time, of course, to understand what impact the new building, and the art institution it houses, will have on the cultural life of New York. But not since the Museum of Modern Art rattled the foundations of the city’s art establishment in the 1930s has a museum seemed so in touch with the present. Poised at one edge of a city struggling to regain its creative momentum, the New Museum building embodies a leap of faith. It suggests a breathing space somewhere between the innocence of New York’s artistic past and an encroaching money-driven cynicism. It’s hard to think of another architect who’s been able to capture that uneasy optimism with such grace.