Good Afternoon, Wolfeye,
I hope this doesn't end up being a duplicate post. I just bumped the wrong key and apparently lost a multi-paragraph response to your questions.
The St. Louis Zoo is terrific. It is located in the southwestern corner of Forest Park at the western edge of the city. The park itself is generally regarded as safe, at least in daylight hours. The zoo, with its large number of family visitors, is even safer--and it's free. Parking in the zoo lot, however, is not free. The last time I was there (several years ago), I recall thinking that the parking fee was high. Perhaps there is a web site with specific information. There is also free parking on park roads near the zoo, but the spaces close to the zoo and the nearby Art Museum tend to fill up early.
I agree with the recommendation of the National Museum of Transport which is well west of the city itself, out just past Interstate 270. The Arch grounds and Laclede's Landing downtown offer plenty of opportunities. The Missouri Botanical Garden (Shaw's Garden) is a great place for photography. There is a modest admission charge there, but parking is free. I've heard that there may now be a tripod permit required. Unfortunately, some of the city near Shaw's Garden has deteriorated in recent decades and isn't particularly safe, but the garden and its parking lot are enclosed areas.
Schiller's on Manchester to the southwest of the city limits has some used equipment, mostly 35mm stuff. They have vastly reduced their inventory of film/darkroom supplies and equipment, but they still carry a decent selection of 35mm and MF film.
You didn't ask, but I'd recommend Allied Photocolor for film processing. Allied is located on Forest Park Boulevard near Sarah. That's about halfway between downtown and Forest Park and just a bit north of Highway 40 (Interstate 64). Allied is worth a visit just to see the large display prints and transparencies in the reception area.
Be warned that several miles of Interstate 64 are completely closed while being rebuilt. The section affected is a few miles west of the city. There are also, of course, related traffic problems on other streets in the area, especially during rush hours.
Feel free to PM with any additional questions.
Konical