The Gateway Arch. It's the tallest national monument in the United States and stands 630 feet tall along the banks of the Mississippi River. The span of its legs at ground level is 630 feet, the same as its height. It weighs 17,246 tons. Nine hundred tons of stainless steel was used to build the Arch, more than any other project in history. In order to ensure that the constructed legs would meet, the margin of error for failure was 1/64th of an inch. The Arch sways a maximum of 18" (9" each way) in a 150 mph wind.
In my humble opinion the Arch is a must-stop point of interest if you're passing through the area...in search of amusement park thrills, of course.
The Arch is quite a sight and the trip to the top is a thrill ride of sorts itself. The views are spectacular and the whole thing just might teach you a little bit in the process. Exactly the type of thing I like to add to the Special Features section of the site - and here it is. Enjoy the photos.