Hot Springs National park in the city of Hot Springs, Arkansas is both the oldest and smallest US National Park. As you can probably guess, the order of the day are steamy hot springs but unlike many other national parks, a lot of Hot Springs National Park's charm lies not in its nature (which of course is excellent) but in its history. The entire north end of the city of Hot Springs, Arkansas is encapsulated by the park and you can visit many of the historic bathhouses like Lamar and Ozark bathhouses, and the especially beautiful Fordyce Bathhouse.
If you'd rather escape a bit into the woods, well, there are plenty of areas for that too. The northern end of the park is full of pine forests and you can see animals like squirrels and raccoons. There's one trail called the Hot Springs Mountain Trail that's especially nice; it takes you up the ridge and back down through the forest and doesn't take more than an hour or so (if that) to complete.
It's one of the best places to visit in Arkansas and gives you insight into what life was like in the early days of the state (the city of Hot Springs itself owes its existence to these natural thermal baths). The park itself is free but there's a small charge ($5-10) if you want to camp inside the park.
The Garven Woodland Gardens are beautiful botanical gardens just a few minutes outside of Hot Springs, Arkansas. The gardens are located on a scenic plot of land jutting out into Lake Hamilton and has tons of different gardens and some absolutely sublime views of the surrounding lake and mountains.
One of the coolest and most beautiful parts is the Anthony Chapel Complex. Anthony Chapel is a glass-enclosed chapel set in the middle of a gorgeous wood that's very reminiscent of (and just as beautiful as) the famous Thorncrown Chapel in Eureka Springs. It's a popular place for weddings, but just coming across it as you wander through the gardens is a pleasure indeed.
Another of my favorite corners of the Garven Woodland Gardens is the Weyerhaeuser Bonsai Garden. The Bonsai Garden is, as you can imagine, a Japanese-style garden that has rock gardens and many intricate miniature trees. There's also a visitors center related to the Bonsai Gardens but we didn't visit when we were there. My recommendation? Get lost! There are pine woods, pavilions, bonsai trees, amazing churches, waterfalls, and tons and tons of wildflowers. Access to the Garven Woodland Gardens is free almost every day of the year, so just take a snack and a bottle of water and spend the afternoon getting lost in the glory of the Arkansas wilderness.
Lake Catherine is located in Lake Catherine State Park just outside of Hot Springs, Arkansas. If you're planning on goes to Hot Springs to see the national park and the historic baths, I'd suggest planning a weekend afternoon relaxing out by Lake Catherine as well. As part of the famous Diamond Lakes in the Ouachita Mountains, Lake Catherine is a perfect place to go fishing, swimming, boating, hiking, or to just relax with a picnic and some sunscreen.
One of the best things to do at Lake Catherine is to go boating and fishing. There's a shop at the marina where you can buy bait and thy have some pretty unbeatable deals on boat rentals. You have basic fishing boats for $20 a day, kayaks, slips, and even big party barges for $200 day. That' a plan right there! Get some friends, stock up on food, drinks, and good music, and spend the day enjoying the sunshine and mountain views from your own party barge!
Hiking is another of the more popular activities at Lake Catherine. There are three or four trails you can hike (there are signs at the park to help you out), but make sure to pick one that passes by Falls Creek Falls, a quiet waterfall hidden back in the woods. To put it simply: check out Lake Catherine if you're visiting Arkansas in summer. You won't regret it!
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.
The most famous (and, at 192 miles, longest) trail is the Ouachita National Recreation Trail, but a shorter and more interesting choice might be the Womble Trail, a 37-mile stretch that runs along the bluffs above the river and offers absolutely stunning view. Don't worry though, there are plenty of shorter routes and combinations that you can easily to in a few hours.