Jefferson National Expansion Memorial. Includes Arch, IMAX about Lewis and Clark, documentary about building arch, Westward expansion museum, Old courthouse where Dred Scott decision made/doc about Dred Scott, .
This is so much MORE than roadside Architecture, but I include it here as a personal favorite. I dare you to drive in sight of it and not turn your head! I grew up in suburban St. Louis so I have a warm affinity to the "Arch". It's creator Eero Saarinen, is one of my favorite modern Architects.