Frank Lloyd Wright's landmark museum building is visited as much for its famous architecture as it is for its superlative art. Opened in 1959, shortly after Wright died, the Guggenheim is an icon of modernist architecture, designed specifically to showcase -- and complement -- modern art. Outside the curvaceous building, Wright's attention to detail is strikingly evident -- in the portholelike windows on its south side, the circular pattern of the sidewalk, and the smoothness of the hand-plastered concrete. Inside, under a 92-foot-high glass dome, a ¼-mi-long ramp spirals down past changing exhibitions. The museum has strong holdings in Vasily Kandinsky, Paul Klee, Marc Chagall, Pablo Picasso, and Robert Mapplethorpe. In its Tower galleries, double-high ceilings accommodate extraordinarily large art pieces, and the Tower's fifth-floor sculpture terrace has a view overlooking Central Park. On permanent display, the museum's Thannhauser Collection is comprised primarily of works by French impressionists and neo-impressionists including Matisse, van Gogh, Toulouse-Lautrec, and Cézanne. Changing exhibitions focus on artists ranging from Norman Rockwell to Jeff Koons. COST: $15; Fri. 6-8 pay what you wish. Subway: 4, 5, 6 to 86th St.