Two hours west of Kansas City is where the prairie begins... or rather (since it's May and we had a lot of rain) green hills as far as the eye can see... alternately evoking comparisons with the Swiss alps (but a little less hilly) or Ireland (but with less drunk Irishmen). The Konza Prairie Biological Station (that's what it's officially called) is part of the Flint Hills and basically a huge chunk of tallgrass prairie (there's even a herd of buffalo, although in a not publicly accessible part).
We took a 3 hour hike along one of the hiking trails and I loved it - the husband mostly enjoyed the fact that we saw a weird lizard (a "horned lizard", apparently) and that we had packed snacks and plenty of water...