Answer:
Something wholly unreal, yet seems real to I. Think my friend, tell me where does it lie?
What is as big as you are and yet does not weight anything?
In marble halls as white as milk, lined with a skin as soft as silk. Within a fountain crystal-clear. A golden apple doth appear. No doors there are to this stronghold, yet thieves break in and steal the gold.
When you stop and look, you can always see me. If you try to touch, you cannot feel me. I cannot move, but as you near me, I will move away from you.
I am the greatest teacher out of them all, but alas in the end I kill my pupils.
What did the piece of wood say when he saw the screwdriver and screws approaching?