Crowley's Ridge State Park is one of Arkansas' most popular natural areas and is nestled in the foothills of the Ozarks in the northwest corner of the state. If you're thinking about visiting Crowley's Ridge, the most popular things to do are fishing (there's a stocked lake!), hiking, and checking out the historical sites. The park is named after Benjamin Crowley, one of the first settlers in the area. You can still visit his log cabin and homestead and get a glimpse of what life must have been like in the pioneer days.
If you're a hiker, I'd recommend the Spider Creek Trail. It begins at the picnic area and takes you through about a mile of forest and meadows full of wildflowers. One tip: don't forget to bring insect-repellent, especially in springtime! If you like fishing, there's a lake stocked with catfish and they have boat rentals at the marina area. If I remember correctly, they rent fishing boats for something incredibly cheap like $7 a day, so, if you want to go fishing with the family, this is probably the best place to go.
The park is open year round and there are different fees depending on what you want to do. If you just want to hang out and go for a swim, it's something like $2.