Peter Eisenman's Berlin/Holocaust memorial Light and Shadow. I like the way the structure of the building creates strong impressions of light and dark. Also the juxtaposition between the natural and man-made forces interests me.
Unity and repetition. A great example of Unity; with the repetition of the arc structure and reflection, place this image in a way that brings them all together. The spacing within the shadow on the wall also creates the sense of great proximity and mood.