This $818 million, 3.1-million-square-foot colossus is the largest federal building to be constructed in the Washington area since the Pentagon, and the first to be designed for use by both the government and the private sector. A blend of classical and modern architecture, the Indiana-limestone structure replaced what for 50 years had been an enormous parking lot, an eyesore that interrupted the flow of the buildings of Federal Triangle. The Reagan Building houses the Environmental Protection Agency, the U.S. Customs Service, and the U.S. Agency for International Development. The D.C. Visitor Information Center (202/328-4748. www.dcvisit.com), located here, is a convenient place to pick up brochures, see a free historical video, and get tickets for tours or evening performances. There's also a multilingual touch-screen computer kiosk with information about the city. Hours for the visitor center and its gift shop are 8:30-5:30 weekdays (March 15-Labor Day) and 9-4 Saturday. Labor Day-March 14 weekdays 9-4:30. The building has a food court on the lower level, and a theatrical group, the Capitol Steps, performs works of political satire here on Friday and Saturday nights at 7:30.