I don’t like treadmills, either. Are there any public buildings with stairways? You could always just carry a pack up and down them - of course, that’s not exactly the same as climbing a hill.

The foothills sound like the best bet. Alternatively, if GSMNP has some less rugged trails, you could camp at the park (or in a motel in Gatlinburg) and do dayhikes with a full pack on those trails.

I’ve heard, from a friend who’s been there, that the Roan Highlands isn’t too bad in terms of big climbs - I’ve never been, and I’m not sure he’s right.

If you take it slow, and have built up your legs on flatland hikes, you’ll probably be OK taking on some fairly rugged terrain without too much trouble. You’ll just find yourself stopping fairly often to catch your breath, but that’s not the end of the world.