Answer:
In a tunnel of darkness lies a beast of iron. I can only attack when pulled back. What am I?
I have 24 keys but cannot open any locks. Sometimes loud, sometimes soft. What am I?
In many hall ways you would stand if not with me in hand.
Flat as a leaf round as a ring. I have two eyes but can't see a thing.
I have no voice but I can teach you all there is to know. I have spines and hinges but I am not a door. Once I've told you all, I cannot tell you more. What am I?
A little house full of meat, no door to go in and eat.