Hermann - - we went there last summer. There are a bunch of wineries there, so mostly it's for adults. We first went to the Hermanoff Winery. They have a self-guided tour and a tasting that you may choose up to a certain amount of wines to taste.
Then we drove a little further out and went to the Stone Hill Winery. It was a guided tour, which cost money, but then the tasting room was the best tasting we've ever done (and we've done a few!!!!). My husband then went away with 12 bottles of wine, and a special bottle of grape juice for our very patient 8-1/2 year old niece. My MIL bought several bottles, as did our older daughter. Some of those bottles that my MIL bought, reappeared at Christmastime as gifts.
If you have children in your party, Hermann might not be a lot of fun.
I don't think I saw Six Flags Over Mid-America listed, which is off I-44 southwest of town. There's a water park there now, too. I haven't done this in years, but my daughter and her husband like to go to Six Flags.
Also, down in Bonne Terre (southwest of St Louis, even further south of I-44) is Bonne Terre Mine. A college friend of mine raved about it a few years back. http://www.2dive.com/btm.htm This is a mine in which you can go diving in.
Donna