Oahu, Hawaii
When the Ko'olau golf club opened, the local section of the Professional Golfers' Association sent representatives to rate the difficulty of the course. They came up with a "slope rating" of 162. PGA headquarters said that was unlikely, since the upper limit for difficulty is usually 155. So it sent a delegation from the national office to amend the rating. The delegates ranked it even higher, at 172. Though the course underwent alterations in 1998 to make it easier to navigate (it's now rated 155), the 80 bunkers and six rain-carved ravines still inspired former U.S. Open champion Scott Simpson to declare it "the hardest [course] I've ever played. It's a monster and it's beautiful all at the same time."