Road trip: DC to Knoxville, TN
 

Leaving on Thursday afternoon from DC towards Knoxville Tennessee, coming back on Sunday staying somewhere in our way and arriving Monday. We are considering staying in Roanoke the first night so that on Friday morning we can see/visit some natural scenery close by Roanoke, so far Dixie Caverns is about the only place that we’ve found close, any other suggestions?

Also on our way back to DC we were wondering where to stay (not Roanoke). A small detour from I81 will be OK if it is worth it. We are mostly interested in nature (not necessarily hiking) & photography.

Thanks!
Oh, and also any "must do's" in Knoxville will be appreciated!