Keeneland, the race track in Lexington, is beautiful. The Ky Horse Park is really nice as well...haven't been there in years. If you are interested in horses at all, you can always try to call up some of the horse farms and see if they will give you a tour. Not sure about 6 Flags, but there's Kings Island in Cincinnati that's not too far up I-75.
Have fun, I went to UK, it's a beautiful city.