Answer:
As round as an apple. As deep as a cup. All the king's horses can't pull it up.
You need a key to receive an answer from me. The answer you'll find is straight from your mind. What is it?
Who eats a lot of iron without getting sick?
What I am filled, I can point the way. When I am empty. Nothing moves me. I have two skins. One without and one within.
I cannot be felt, seen or touched. Yet I can be found in everybody. My existence is always in debate. Yet I have my own style of music.
What never gets any wetter no matter how hard it rains?