Duck River Complex State Natural Area - Cheeks Bend Bluff Trail (Tennessee)
This is a great short hike less than an hour from downtown Nashville. There is even a cave passage (unlit, so bring a flashlight or use your camera flash as I did) that you can pick your way through to get down to the river. Lots to see, both big and small. Do keep an eye out for snakes, though, as we found one on the rocks as we came out of the cave above the river (much to Lauren's dismay since she had been standing right in front of it as I took a photo of her and my ex-husband). :-)