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They're only odd because you won't have a lot of time for significant side trips given the distances involved and the type of vehicle you'll be driving, but I found Crater of Diamonds State Park in Arkansas interesting as were Hannibal MO (Mark Twain) and Springfield IL (Lincoln). An 'oddity': if you want to avoid St. Louis, you could head up through west-central Missouri and include both a second Columbia and a second Springfield. More to your point, once you're into southwestern Arkansas, there will be more national forests and state parks for those short walks

AZBuck