15th St NW at Constitution Ave; closest Metro Smithsonian. April–Aug daily 8am–midnight; Sept–March daily 9am–5pm. Admission free.

The Mall's most prominent feature, the Washington Monument is an unadorned marble obelisk built in memory of George Washington. At 555ft it's the tallest all-masonry structure in the world. Volunteers started work on it in 1848, but various internal arguments, and later the Civil War, so disrupted construction that it wasn't completed until 1884. When the US Government took over the project in 1876, they used marble from a slightly different source; the transition line where work resumed at the 150ft level is readily apparent.

To visit the monument pick up a free ticket from the 15th St kiosk (on the Mall, south of Constitution Ave), which allows you to turn up at a fixed time later in the day. The elevator up takes seventy seconds and deposits you at the 500ft level in order to enjoy the monument's panoramic 360° views of the city.