The National Monument stands as the tallest building in Washington, D.C. At 555 meters, the National Monument is made entirely of marble and granite, and took 36 years to complete. When it was completed in 1884, it was the tallest building in the world. This building in Washington remains one of the most prominent tourist attractions in the city and the world, and is visited by hundreds of thousands of tourists every year. This monument is located in a central area of the city near Lincoln Mausoleum, so don't miss it if you are in the States!