Thomas,
It is not just obstructions but use whatever term you like. Tom Doak called “short grass” one of the best hazards and I agree but those who don’t really understand GCA would never call it that and that is fine. The point of the thread is that on the greatest holes there is ALWAYS some distinct or memorable feature that makes it special and most of the time it is some kind of hazard (or whatever you want to call it - penalty area, obstruction, mound, hollow, OB, wall, lake, stream, ocean, tree, building,...). We sometimes forget golf was all about circumventing hazardous challenges and trying to get the ball in a hole in the least amount of strokes. The best holes were the ones that presented the best test and the most interest. But I am sure we will debate that as well 😊