I had thought of an idea for a campaign setting that I wanted to DM in many years ago, which basically entailed me not creating the world at all until we played in it, allowing all details to be designed as we played, catering to what the players want. Whatever they expressed interest in, I would put in it. If I heard someone say, "That would suck if we ran into xxx," well then they would run into it. Never got to do it until recently, and it is by far the most successful campaign I have ever run. My players actually know about the world because they had input in it. They have designed and built villages and towns, created the cultures and helped along the politics. I called it Soul's Fury because it was to come from the heart and imagination of my players (the Soul part), and the Fury part because I get to lash out at them for wanting something I didn't (lol).