The Buffalo National River is a beautiful river that runs from the Ozarks in northern Arkansas all the way down to the Ozark National Forest. If you're the outdoorsy type, this is your place. You can do literally anything: fishing, camping, horseback riding, kayaking, tubing, etc. I'd personally recommend grabbing and inner-tube or a canoe and spend the day lazing down the Buffalo River and taking in the gorgeous forest scenery and the fresh air.
If you're planning on going tubing, kayaking, or canoeing, there are a number of places where you can drop in. The most popular are probably the Tyler Bend Visitors Center and the Pruitt Landing, my personal favorite. However, many people choose to drop in at Boxley Bridge a.) because it's easy to get to, and b.) that's where a lot of hiking trails like the Low River Trail start. If you're going with a mixed or large group, I'd definitely recommend starting at Boxley Bridge.