Scenery from Missouri. The Gateway Arch in downtown St. Louis as seen from the Mississipi river. The St. Louis Gateway Arch is an elegant monument to westward expansion in the USA. Located on the banks of the Mississippi River in St. Louis, Missouri, the 630-foot tall stainless steel arch rises above the city skyline. Underneath the Gateway Arch is the Museum of Westward Expansion. The arch was opened to public in 1967.