If you can find the time, go visit Forest Park. The Zoo, the History Museum, The Art Museum, The Jewel Box, Art Hill, The Worlds Fair Pavilion, etc. Except that this time of year during weeknights, everything closes around 5pm...so...get off work early.
I recently went to the History Museum and saw some of the images from the Worlds Fair in 1901 that was held here...and the buildings that they built were ASTOUNDING. It seriously looked like ancient Rome in its heyday. Sadly, nearly every single one of those buildings was torn down because the city couldn't afford to keep so much land unused. They actually charged (and made $$$ off of) admission to watch the buildings be torn down.