The Universe
Endless: The universe is an unimaginably sparse void of infinite space, littered with stars, planets, and various detritus.
Limited: The physical universe in your campaign world might be smaller in scope yet far more fanciful. For example, Norse cosmology describes nine worlds connected by an immense ash tree. How does that fit into your science fantasy story?
Bizarre: Sometimes the universe is more complex than the previous two categories, or possibly nested within multiple realities and timelines. What if the universe the PCs first know is in fact a magical or technological simulation of such complexity that its inhabitants are unaware that they exist as an artificial consciousness? Perhaps this is even where your PCs first meet before transitioning into another reality.