All Wildspace is bounded by crystal shells or crystal spheres. Inside the crystal sphere is the vacuum of Wildspace, the planets, and stars. Outside the crystal sphere is the rainbow ocean of phlogiston and more crystal spheres. The size of a crystal sphere is determined by the size of the planetary system inside. Usually a sphere has a radius at least twice as big as the orbital radius of the outermost celestial body in the system ( i.e., the distance from the shell to the outermost body of the system is the same as the distance from that outermost body to the center point of the system).
Because of their great size, the outside of a crystal sphere appears perfectly flat. The curvature is so gradual that it is completely undetectable to anyone who is close enough to see the crystal sphere through the obscuring phlogiston. The sphere consists of an unbreakable, dark, ceramic material of unknown origin.
The crystal shells are uniform throughout space. All appear as great, dark, featureless spheres of unidentifiable matter. The crystal spheres are definitely solid. They have no gravity along either their interior or exterior sides (an exception to the rule that all large objects have gravity). No magic has been found that can damage or alter the surface of a shell, except for those spells which cause portals to open. Even this, however, is believed to nothing more than an artificial triggering of a natural phenomenon, since portals also occur naturally and seemingly at random. They are apparently immune to the effects of wished and even the wills of the outer planar powers.