^Damn, you really brought this thread back from the dead. I don't want to step on Robb's toes, but since I'm a St. Louis area native I hope it's OK to chime in.
As far as things to do in St. Louis, here are some of the most popular activities:
The Gateway Arch. Go to the top if it's convenient and won't eat up your day. https://www.gatewayarch.com/
We have a fantastic zoo, which has free admission and is located in iconic forest park.https://www.stlzoo.org/
We have a nice baseball stadium and there is a huge Cardinals following in the area, if you're into that kind of thing. (I'm not)https://www.mlb.com/cardinals
I haven't been in probably ten years, but TPR members love City Museum, which is more or less a playground for all ages.https://www.citymuseum.org/
Grant's Farm is pretty much like a large outdoor petting zoo with a couple beer samples thrown in. If you're going to go on a weekend get there a half hour before opening if you want to get in easily.https://www.grantsfarm.com/
Speaking of beer, the Anheuser Busch brewery tour is really interesting and it takes about an hour. You get a couple free samples at the end with a chance to purchase more.https://www.budweisertours.com/
If you're looking for a quick pizza, try Imo's. It uses provel cheese with a cracker crust and the flavor is unique to the area. It's worth a try:https://www.imospizza.com/
If you're looking for something else to eat, just let yelp lead the way. It always steers you in the right direction.