Yikes! So many great ideas!  I will support for this coming month the WALLS suggested by inshaala.   Why? Walls real or perceived are a true creative challenge.

Walls  may be foundations, supporting, barrier or protection...on and on...and perceived ones will take an image that really "speaks" to the viewer to see the meaning.   I will go for walls on this one.

I can add no new ideas..most are covered already.  And, I have no walls yet thought of.   Tom.