At 630 feet, the Gateway Arch is both the world's tallest arch and the world's tallest man-made monument.
St. Louis is well known for this monument, which was built as a monument to those who had explored the frontiers and enabled the western expansion of the United States. It towers over the city skyline, demanding to be noticed and claiming its dominance. The Arch is located in Gateway Arch National Park, a riverfront plot of land with small ponds, trails, some parking areas (though you may need to park up to a mile away and walk to the park). You can get some good pictures by riverboat starting just next to the park, and for those seeking a more thrilling angle, you can take a helicopter tour instead. For a nice view of the city without the Arch, you can pay to ride a tram inside the Arch and take a picture out one of the windows at the very top.