Most people on this thread seem to be giving nominations for poor pieces of ground, not average.
What always fascinates me is when a course is special, yet the terrain seems no different than many others in that region. Oakmont sure seems like basic western PA land, yet it is truly one of a kind.
Is the land for Merion particularly special? It looks like basic parkland to me, but the result is certainly special.
I was always fascinated by Tom D's description of St. George's in The Confidential Guide, the way he said it played along the hills and valleys, rather than the more traditional up and down. I'd love to see the course someday so that I can actually understand what he means!
I'd love it if some of the architects could nominate some courses that appeared to be on really special ground, but are actually quite difficult. Doonbeg and Old Head are two that seem to have been mentioned in this regard.