Summit Park Trail at Mount Nebo State Park (Yell County, near Russellville) is a really cool trail. This hillside trail has lots of interesting rock formations–from rock gardens to massive boulders–as well as beautiful stone staircases, great views, and much more!
My girlfriend and I took a walk on the trail on an August afternoon. The temps were moderate at first due to some recent rain. It warmed quite a bit before we were done, but it was still a beautiful and enjoyable hike.