Answer: The Gateway Arch

The Gateway Arch, also commonly called the St. Louis Arch due to its geographic location, is an enormous monument located in the city of St. Louis in the U.S. state of Missouri. It’s the world’s tallest arch, the tallest monument in the western hemisphere, and the tallest accessible building in Missouri. While those particular bits of trivia might be new to many readers at minimum, most people are familiar with the big ol’ arch in St. Louis as it features prominently in photos of the city and is featured heavily in tourism promotion for the area.

Less familiar to readers outside the region is that the arch doesn’t exist for the simple sake of being a city landmark and tourist attraction, but is a monument to the westward expansion of the United States and is the crown jewel of the Jefferson National Expansion Memorial, a president under which the United States saw unprecedented expansion.