As for "domains":
Planes of Law mentions the Citadel of Stars, without really going into detail. For the Lunia write-up, I've gathered a few ideas:

The Citadel of Stars consists of a cluster of almost impossibly high towers of violet crystal, rising directly from the sea. The entire structure shimmers with a faint light.
While there are few (or none at all) entrances at see level, the citadel has a myriad balconies for flyers to land, some large enough for dragons, giant birds or other large creatures.
It becomes immediately obvious that this is the home of the Trumpet Archons: the entire structure is hollow, and the interior of the towers is kept empty, gigantic tubes the size of mountains that allows the sea wind to rise through them, playing the entire citadel like a pipe organ.