Sci-fi / Fantasy World-Building Exercise

World-building: it's the ultimate brainstorming session where everyone participates in creating a sci-fi and/or fantasy world. We'll start by having participants shout out ideas for settings and then decide on one or more. For example: perhaps we set the story on Earth 250 million years ago on the supercontinent Pangea or in a solar system in the process of forming or in a two-dimensional universe. We'd do the same thing for characters, conflict, plot, physical laws, etc. If we want the character to be able to wield magic, we come up with unique ways for that magic to work. Perhaps it costs a body part to cast magic. Perhaps someone close to you must die to wield a really powerful spell. Or something else entirely. We'd spend some time creating a detailed and very robust world. Then, we'll move on to further brainstorming regarding different aspects of the story, thus bringing it to life. This would be a mostly verbal exercise, with our results getting put up on a white or chalk board. Just what crazy things will we come up with?