The Loop is a living architectural museum, where shimmering modern towers stand side-by-side with 19th-century buildings. Striking sculptures by Picasso, Miró, and Chagall watch over plazas alive with music and farmers' markets in summer. There are noisy, mesmerizing trading centers, gigantic department stores, internationally known landmarks like the Sears Tower and the Art Institute, and the city's newest playground, Millennium Park. Rattling overhead, encircling it all, is the train system Chicagoans call the El.