“I was playing with the idea of Rokugan (of which I know little) or Ravenloft (the campaign setting that made players afraid of fog), but since I am getting a lot of feedback from the Spelljammer community, I will go back to that and briefly, briefly, speak about the Rock of Bral.
Running a space-based campaign is difficult, because there is no central point, no home town. You can have a Shadowdale or Waterdeep as a home in the Realms, a place where you know everyone (if not trust everyone). Where you can stock up and recover and repair and maybe get a house to put all your stuff in. In space, the role of your house is taken up by your ship, but then where do you interact with others? Pick up stories? Go out for a few drinks?
Hence, a (semi) portable city, suitable for placement in your campaign setting. A place where other spelljammers can dock, where adventures can begin, and where adventurers to retire to. The shape of the map gives it a general Waterdeep vibe (longer than it is wide), but the nature of space and what has been termed “Grubbian Physics” created a different world indeed.”