I asked him, “What makes a place fun?,” which happened to be the title of his talk. His complete TEDxBoulder talk can be found HERE . It’s great.
Note that David’s answer to the question of what makes things fun is reminiscent of the benign violation theory of humor’s notion of simultaneity. That is, there is something both real and unreal about a place that helps make it fun. Said another way, there is some ambiguity about the place that the observer can make sense of, and when that occurs people delight in that place.