The Falls of the Ohio State Park sits on the Indiana side of the river, but it is so closely tied to Louisville's history that it belongs in any account of the city. The "falls" are actually a series of rapids formed by a rocky limestone ledge — just a two-foot drop at normal water levels, but enough of a barrier to stop river traffic and create the portage point around which Louisville was built in 1778.
When the river is at low-to-normal levels, the interpretive center walk leads out onto 220 acres of exposed Devonian fossil beds — coral, crinoids, and molluscs from the ancient tropical sea that covered this region 390 million years ago. The fossils are so numerous and well-preserved that you walk across them without trying. The interpretive center explains the geology clearly. Easily combined with a day on the Louisville waterfront.