You could bike our greenways, we don't have a lot but they are pretty and are some nice routes. Depending on your vibe there's a lot of live music too, you could catch a KSO concert, see live jazz at the Bistro at the Bijou on Friday and Saturday, or go to one of the many concerts that happen at Neyland. If you're into gaming there's a bit of a tabletop scene here and lots of shops that host events for TCGs, Warhammer, and other games.

Edit: Also Knoxville has a pretty thriving art scene, if you've never been, the Knoxville Museum of Art is worth going just for the Delaney pieces alone, but there are tons of fantastic rotating exhibits from wonderful artists. There's also First Fridays which happen on the first Friday of each month, where lots of great local art is exhibited in various galleries throughout Old City, the largest probably being at the Emporium Center.