In Down Below, Joan Aiken comments on different issues facing us today.  It talks about things getting in the way of what we want, and what we’re working for.  It compares the crossword puzzle of ladder and corridors to obstacles in our everyday lives.  These things prevent us from getting where we want to go, and from things we want to accomplish: making achieving these goals so much more enjoyable.  It also talks about the hold of the ship, its awful conditions, and also the stowaways who are stuck inside.  This brings up the point of prejudices toward minority groups, or just unfair treatment to anyone in general.  Having these people in damp moldy areas is obviously an unfair treatment toward them, allowing this to be heir only option to escape to a different place, providing them with freedom.  So the overall message of the poem is about the decisions that we are willing to make to achieve something, and the obstacles that stand in our way.