If a door doesn't open to anything, is it still a doorway? Does the word "door" refer to the physical object, the frame and the lintel and so on, or does it refer to the function, the passage into another space?
If we cover cinder blocks with bricks, then which is the wall? The layer of cinder blocks or the layer of bricks? Or both (or neither)?
What is keeping us out, and what is letting us in? What walls separate us? What doors are open to us?