We made reservations for the St Louis Arch (also known as the Jefferson National Expansion Memorial). It was great! There is a visitor's center under the arch and plenty to keep you busy while waiting for your turn.
The ride up the arch is scheduled and you buy tickets for a certain time (can buy online or over the phone to avoid the long lines). A few minutes before your scheduled time you gather in a line and watch a video about the arch. Then it's almost like a Disney ride - there are 8 "pods" which hold 5 people each. You wait outside your pod door and then climb in. Although they don't warn you - I'd really not recommend it if you are claustrophobic...or over 5'10" tall !! I've forgotten the exact times - but it's about a 4 minute ride to the top and a 3 minute ride back down. I'd love to see a replica of how the "elevator pods" maneuver up the arch as it is quite a feat.
The top of the arch was great and it was a clear morning so we could see quite far.