Answer:
Many have heard it, but nobody has ever seen it. It will not speak until spoken to. What is it?
I grow where no flower grows, where no light touches the walls, up or down, that I don't care, was here before people were.
I turn around once. What is out will not get in. I turn around again. What is in will not get out.
I am whole but incomplete. I have no eyes, yet I see. You can see, and see right through me. My largest part is one fourth of what I once was.
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.
If you count 20 houses on your right going to the store and 20 houses on your left coming home, how many houses did you count?