A jewel has been set in the emerald-necklace-like Brooklyn Bridge Park: an acrylic glass pavilion by Pritzker Prize–winning French architect Jean Nouvel. Nestled on the Brooklyn side of the East River in New York City, the $9 million steel-frame pavilion—and the colorful merry-go-round it houses—sits on a rocky outcropping with sweeping views of the Lower Manhattan skyline. The carousel, built in 1922 by the Philadelphia Toboggan Company, fell into disrepair after it was discontinued as a ride at an Ohio park. In 1984, Brooklyn-based artist Jane Walentas and her husband, property developer David Walentas, bought the derelict carousel, and Ms. Walentas worked to restore it to its original splendor. Then Nouvel designed the vitrine. “I wanted to create a fragile monument on a very violent site,” the architect explains. “I see this contrast as very poetical, and I wanted to keep that contrast.” Eight-foot-by-3-foot butt-glazed glass on the pavilion's northern and southern exposures, and operable accordion walls on the eastern and western facades, protects the carousel. For a cool two dollars a ride, children of all ages can board the carousel and take in the panoramic views it offers. At night, a scrim lowers from the pavilion's ceiling. Projected silhouettes of the herd gallop in an endless loop, a magic lantern on the riverbank.