March on over to Scott Air Force Base, tour the site and try to understand what being a member of the military is like.
You'll have sightseeing choices galore when staying in O'Fallon. Scott Air Force Base is a great place to begin here, but there are numerous other worthwhile attractions to check out. O'Fallon Family Sports Park, McKendree University, and St. Clair Bowl are not far from the military installation and will top off your day nicely.