This is a 1/2 mile model of the Lower Mississippi, and it was very cool! You can learn a lot about the history of the river here.
It starts in the watersheds of many rivers like the Ohio, the Missouri, and the Tennessee River (we're talking the Lower Mississippi here, all you Indigo Girls fans who may be humming, "Well, the Mississippi's mighty and it starts in Minnesota, at a place that you can walk across..."). These watersheds are represented by waterfalls over maps:
Then the kids started following it:
About halfway, Gretchen got this shot of the kids with the miniature Mississippi in the front and the Mighty Mississippi behind:
Eventually, we got to the Gulf of Mexico:
And, can I just say that I love my new camera lens: