Great question. The first thing I think of when I see "other-worldly" is Peter Jackson's portrayal of Rivendell, incidentally. Anyway, several places jump out at me. The Smokies under an early-morning or late-evening fog:
Highway 101, wending down the craggy Pacific coast with dropoffs on your right and 200-foot tall trees on your left. Fog in the mornings there, too. But the place that takes the cake is a little back road I got lost on in central Washington near the Yakima River (maybe Willamette National Forest? I don't know, I was lost). The classic cliche of branches forming a perfect arch above the road -- for miles -- coupled with bright sunlight that filtered down, but the trees so well covered the road that I had my lights on at noon. Never gonna forget how amazing that felt.