One of the reasons that Royal Portrush is rightly so highly regarded is because it's an excellent driving course. And one of the reasons why it's an excellent driving course is that it has several holes with, to different degrees, reverse camber fairways. The most prominent example--and probably not coincidentally one of the best holes out there--is number 15. From the back tees, you drive up and over the hill on the left with the fairway always running to the right. The further you go, the more the hole turns and the more difficult it is to keep it in the fairway. As was mentioned above, that's one of the great elements of these kinds of holes--the further you go, the more they often turn, posing a strong trade-off in the club that you choose from the tee.
Other examples on Royal Portrush are 9, 10, and to a lesser extent, 18. 9 is more subtle than 15, although there are also bunkers on the outside if the fairway if you don't cut it enough. The back tee on 10 is so far back that I'm not sure most can even reach the dogleg right from there. But from the further up tees, it's tough to pick a line and the left side of the fairway slopes sharply away.
Not to make this a post about Royal Portrush, but there are a variety of other driving challenges including tight fairways (8, 14), fairways that are tight at normal driving distance and force either accuracy or a layup (1, 2, 4), and holes where you can bomb away, although you'd better roughly hit your line and distance (5, 11, 17). I'm not as big a fan of the course as others, but I thought it was an excellent test of driving and because of this, reminded me more of a US Open course than others I played in the UK and Ireland.