From my mom:
The St. Louis main library was just reopened. It is one of the larger Carnegie Libraries: he donated $1million to build this library in 1899 (I don’t see any other grants that large on the Wikipedia page). I only saw the inside once, in about 1970. Now it has been totally renovated and looks amazing, with all the original marble, stained glass etc. It would be worth a trip, especially if you’re in town.