This museum grew out of a gallery in the studio of the sculptor and collector Gertrude Vanderbilt Whitney, whose talent and taste were fortuitously accompanied by the wealth of two prominent families. In 1929 she offered her collection of 20th-century American art to the Met, but they turned it down, so she established an independent museum. The current building, opened in 1966, is a minimalist gray-granite vault separated from Madison Avenue by a dry moat; it was designed by Marcel Breuer, a member of the Bauhaus school (its manifesto called for architects and artists to work toward "the building of the future"). The monolithic exterior is much more forbidding than the interior, where exhibitions offer an intelligent survey of 20th-century American works. The fifth floor's eight sleek galleries house "Hopper to Mid-Century: Highlights from the Permanent Collection" featuring works by Reginald Marsh, George Bellows, Robert Henri, and Marsden Hartley. Notable pieces include Hopper's Early Sunday Morning (1930) and A Woman in the Sun (1961), several of Georgia O'Keeffe's dazzling flower paintings, and Alexander Calder's beloved sculpture Circus (192 6-31). The second floor picks up chronologically where the fifth floor leaves off, with "Pollock to Today," more highlights from the permanent collection, including paintings and sculpture by such postwar and contemporary artists as Willem de Kooning, Jim Dine, Jasper Johns, Mark Rothko, Frank Stella, Chuck Close, Cindy Sherman, and Roy Lichtenstein. The famed Whitney Biennial, which presents the most important developments in American art over the past two years, takes place in even-numbered years.