No.18 of my 2018 world series challenge is the Washington Monument. The Washington Monument is an obelisk on the National Mall in Washington, D.C. It was built to commemorate George Washington, the first President of the United States. The monument is constructed from marble, granite, and bluestone gneiss. It is both the world’s tallest stone structure and the world’s tallest obelisk, standing 555 feet 5 1⁄8 inches […]