
KC has a nice little monument to the Lewis & Clark expedition... I suppose it's fitting that you have to explore to find it. :)
Just south of the Missouri River (and just southeast of where it meets the Kansas River - it's kinda weird how the directions work out right there - see the map below), there's a series of high bluffs that overlook the river and the old Downtown Airport to the north. It's a great place to watch the airport; there even used to be some of those coin-operated tower viewers there, though they've been taken out in the last 5 years.
Unfortunately, it's also fairly hard to get to. It's at the corner of two fairly narrow and out-of-the-way side streets, and it's not visible from just about anywhere. It's right at the corner where I-35 and I-70 split at the northwest corner of the downtown loop - but it's at the top of the bluff, the road is a good 10-15 meters below, and it's hard to spot anything from the road. The roads that lead to it go uphill, and buildings block the line of sight from any of the direct routes; the only street with a clear field of view is hidden itself, two blocks away from any major thru street.
I found it mostly because there used to be a Howard Johnson's hotel just below the park on the bluff, where ConQuest KC was held for many years.