EricNoah said:Is the Astral Sea like a sea in the sense you sail on it in two dimensions?
hong said:Magitech skyships? They'll have warstriders next....
Burr said:You could always have something like density layers, thus creating multiple two-dimensional sea surfaces (complete with islands, reefs, etc.) within a three-dimensional sea space.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.