Closed indefinitely for elevator repairs. Completed in 1884, 555-foot marble obelisk honoring George Washington, now the world’s tallest freestanding masonry structure. Elevator to museum and observation deck. Free same-day tickets (required) for entry available at the Washington Monument Lodge (15th St. and Jefferson), 8:30 a.m.-4:30 p.m. (arrive early as tickets often run out). $1.50 for advanced reservations online.