The Washington Monument is a pretty impressive structure, located in the heart of the "swamp" of Washington, D.C. It's an obelisk, a four-sided tapered tower with a pyramid on top. It's just about the only time most of us will ever use the term "obelisk."

At 555 feet tall, it was once the tallest building in the world when it was completed in 1884, and is still the tallest building in D.C. It's oddly two-toned: construction stopped at about 150 feet up and resumed a few years later, but with marble from a different source. The shading is noticeable, giving the monument an odd feel, like whe...