Citizenship in the Nation
You can find a list of all the sites on the National Register of Historic Places in St. Louis County at https://dnr.mo.gov/shpo/stlouis.htm. An index to the listings for all the counties and the city is at https://dnr.mo.gov/shpo/mnrlist.htm. You will be surprised at how many there are, but keep in mind that many or most are private and probably not open to visitors.
The NRHP nomination forms that are linked on those pages are chock-full of interesting information about each site.