Darkgate (3.5e Campaign Setting)/Cosmology
From Dungeons and Dragons Wiki
Cosmology
The cosmos of Darkgate is that of almost every other planet. The only difference is that where as most other planets look up and see a bunch of stars with a few planets, a Darkgate resident (even the street urchin would have some familiarity) looks up and says "There is the star so-and-so, it has five planets named this, that, the other one..."
Also, there are many unknown planes where many powerful creatures reside in. Rage, for example, keeps his school in a small quasi-plane. Only ragers, shadowwolves, and Rage know where this school is.