Answer:
I build up castles. I tear down mountains. I make some men blind, but I help others to see. What am I?
While you were folding a letter you got me. Usually you will do whatever it takes to avoid me but now you can't help but find me.
The more you work the more I'll eat.You keep me full I'll keep you neat.
In buckles or lace, I help set the pace. The farther you go, the thinner I grow. What am I?
Taken from a mine and then locked up in a wooden case. I am used by students everyday.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.