We are also "walkers" due to my knees which I think are 20 years older than the rest of me. That said, we enjoy visiting ONP and usually do this:
Day 1, drive to Lake Crescent with stops at Hurricane Ridge and Madison Falls. Stay at the lodge, maybe hike to Marymere Falls or rent a kayak.
Day 2, drive to Lake Quinault with stops for a fairly easy hike in the Hoh Rain Forest and a walk on Ruby Beach. While at Lake Quinault, hike the nature trail, drive the south shore which includes two waterfalls right by the road.
Day 3, drive back home with a stop for lunch at Cascadia Grill in Olympia and a walk at Nisqually Wildlife Refuge. Yes, the drives are not especially scenic, but you are looking at lots of trees, not ugly strip malls.
If you are coming here from Tennessee, you would want to add some other destination to make the trip worthwhile - maybe Mount Rainier and Mount Saint Helens or a few days in the San Juan Islands.