1100 Pennsylvania Ave NW, at 12th St. Closest Metro stop is Federal Triangle. Mid-April to mid-Sept MonSat 10am9pm, Sun noon8pm; rest of year MonSat 10am7pm, Sun noon8pm. Admission free. tel 202/289-4224, www.oldpostofficedc.com
Built in 1899, the fanciful Romanesque Old Post Office , just across from the FBI, is one of the most recognizable of downtown's monuments. Its glorious galleried interior is now known as the Pavilion, in which guise it supports hundreds of shops, stalls and a food court. The more clued-up visitors make a beeline here, rather than to the Washington Monument, for their first aerial view of the city. The clock tower (mid-April to mid-Sept daily 8am11pm; closed Thurs 6.309.30pm; rest of year daily 10am5.45pm; free; tel 202/606-8691) stands 270ft above Pennsylvania Avenue, and the glass elevator ride allows you to see the iron, glass and wood interior in all its fine glory.