Across Manhattan on the East River rise the sleek buildings of the United Nations Headquarters (First Ave. and 46th St. +1 212 963 7713. Guided tours only; Adm. fee). On the east side of Central Park, a grand parade of art museums begins with the Frick Collection (Fifth Ave. at E. 70th St. +1 212 288 0700. Closed Mon.; Adm. fee). Here, works by European masters fill steel magnate Henry Clay Frick’s 1914 Louis XVI mansion. The Metropolitan Museum of Art (Fifth Ave. at E. 82nd St. +1 212 535 7710. Closed Mon.; Adm. fee), with over two million works, vies only with the Louvre for the title of world’s greatest art museum. Farther up Fifth Avenue, the Solomon R. Guggenheim Museum (1071 Fifth Ave. at E. 88th St. +1 212 423 3500. Closed Thurs.; Adm. fee), Frank Lloyd Wright’s striking spiral modern art temple, has been restored. Harlem is the capital of African America, and one of the best ways to sample its variety is to take a tour with Harlem Spirituals, Inc. (1697 Broadway, Suite 203. +1 212 757 0425. Tours are conducted daily, but office is closed on Sun.; Tour fee). Tours include such spots as the Apollo Theater and the Cotton Club.