Once there was a prisoner who was jailed in a dark prison which he thought was a great fortress(堡垒). The cell was dark and wet. There was a tiny window with bars on it. The rest of the cell was so dark that he could not see the other three walls. The only wall he could make out was the wall with the window in it. The only light the room received was from this window. Once in a while the prisoner would manage to climb up to the window and look out on the world outside. If he stretched and looked, he could see a little bit of the life-giving sun out there.
