Answer:
A great mysterious place that the bold have been known to journey into.
This is in a realm of true and in a realm false, but you experience me as you turn and toss.
Up on high I wave away but not a word can I say.
My teeth are sharp, my back is straight, to cut things up it is my fate.
Half-way up the hill, I see you at last, lying beneath me with your sounds and sights. A city in the twilight, dim and vast, with smoking roofs, soft bells, and gleaming lights.
You use it between your head and your toes, the more it works the thinner it grows.