I think it's just too stinking hot and humid this time of year to do much hiking. I recently had family in town for a week and we headed out to The Greenbrier Resort (white sulphur springs, WV)
www.greenbrier.com and did the bunker tour there. It was awesome!! It was only about an hour from Roanoke and easy to find.
We also toured Jefferson's Monticello in Charlottesville and that was great too! About 2 hours from Roanoke.
The wineries are great on a hot day too! My favorite is Chateau Morrissette in Floyd (nice Sunday brunch). Also love Blue Ridge Vineyards (pretty location) in Botetourt County. Never been to Valhalla but my husband has.
Don't forget to eat at The Homeplace if you haven't yet!