Largest National Forest in Arkansas
Lake Ouachita National Forest is a massive stretch (over a million acres!) of pristine forest in central Arkansas, though most visitors choose to visit the National Forest near the city of Hot Springs. Lake Ouachita National Forest is famous for two main reason: it's gorgeous lake perfect for fishing and boating and miles and miles of hiking and biking trail in the wilderness.
As you can imagine, the national forest surrounds Lake Ouachita. The lake has areas for swimming and picnicking as well as a marina where you can stock up on bait and tackle or even rent a boat for a day. I'd especially recommend the second option as a full-day rental of a kayak, slip, or party boat ends up being pretty cheap. It's something to definitely keep in mind if you're visiting Arkansas in the summertime.