The Blade Stair, as Diller Scofidio + Renfro calls it, refers to a four-flight stairway wrapping around a 6-inch-thick steel central wall suspended from the sixth floor. (The final flight, extending from the fifth to the sixth floor’s Terrace Café, is placed on the east side of the 21-foot-wide hall.) The Blade Stair structure stops 1 foot, 6 inches above the ground level, where the gap underscores this technical feat. The steel stair runs are also attached to steel plates at the various floor levels; the treads, risers, and landings cantilever from them, and white oak covers their top surfaces. The two-ply glass balustrades, clamped with stainlesssteel pressure pins, add to the sense of lightness. “It took some acrobatics to make the stair seem to float,“ says DSR partner Liz Diller, who sees this as a “palate cleanser” for the circuit of galleries on either side of this hall, which also contains elevators. The walls surrounding the stair and elevators are surfaced in micro-perforated gray bird’s-eye maple to deaden the sounds of visitors milling about.