Greens.
Most of the truly famous greens discussed and admired here on GCA -- Yale's 9th, some of those at NGLA, the 14th at Augusta, some of the new ones at Ballyneal -- seem to be more "mand-made" than many other features of a course. I always hear/read about "natural green sites" on admired courses, particularly links courses, but the nature of the green itself -- internal contours, false fronts, receptiveness to the kind of shot likely to be played into it -- strikes me as something an architect would put a lot of time and consideration into. That's my vote.