Washington Monument, Washington

The symbol of the city of Washington DC, this 555-foot marble obelisk on the National Mall honors the nation's first president. The cornerstone of the Washington Monument was laid in 1848, but construction was not completed until 1884. About one-third of the way up the obelisk is a visible change in the marble, evidence of the onset of the Civil War. Construction was halted during the war, and when builders returned to the same quarry to complete the project afterward, enough time had passed to cause a significant change in the color. Admission is free, but a 'timed pass' is required for the elevator ride to the top.