If the Des Moines River isn't flooded take time to walk the banks and the sandbars. Due to the many dams upstream, it seems like the Des Moines River varies between complete flood one year to only about two feet of water just to cross the next. If it is low, you should learn how to find geodes, great fun.
Check out bot Bonaparte and Bentonsport and be sure to ask around to find the "Arrowhead Museum".
Locate "Athens State Park" on the Missouri side. Visit...locate the information center and enjoy. Trails there really worth walking.
I've never spent time in Shimek, though intended to on many trips. Should give you an idea how much I enjoyed the other stuff.