Crystal Spheres

Each universe's Material Plane exists within a Crystal Sphere - a large orb of solid magical energy that separates Voidspace from a universe's Wildspace. This crystal sphere is impermeable except at certain locations where the sphere has been Breached by powerful magic. The magical power to breach a crystal sphere is of a level usually only held by gods, though some particularly powerful mortals in certain universes can attain the power required.

Even once breached, there are still certain restrictions on what can pass through a crystal sphere:

• Phlogiston gas will disappear if captured and brought into a sphere.

• Deities and Avatars of Deities are instantly destroyed if they attempt to leave their sphere.

• Magical Artifacts (items powerful enough to resist destruction in all ways but one) cannot be brought through a portal in either direction.

It is important to remember: once you leave a crystal sphere, you are cut off from everything and everyone back home. There is no magic that can connect back to your home world, and no way to access another plane in Voidspace. Priests are cut off from their gods, magic items relying on pocket dimensions cease functioning, and spells that open planar portals fail. Those with strong grounded ambitions and connections may regret leaving them behind.

The Phlogiston

Between the spheres, stretched out across Voidspace, are rivers made of a highly flammable rainbow gas called Phlogiston. The Phlogiston rivers flow rapidly through Voidspace at varying speeds, like rivers of water running down and around a mountain. The flow is difficult to chart, and changes are nigh impossible to predict. However, Phlogiston does seem to gravitate specifically towards breached crystal spheres.

Spelljammers can ride along this flow, allowing travel speeds far beyond what is possible within Wildspace. Journeys that would ordinarily take millennia instead only take months, weeks, or even days, depending on the speed and size of the flow, and the distance between spheres.

Unfortunately, this means that any unbreached crystal spheres are nigh unreachable by spelljammer. Spelljamming Helms are specifically designed to take advantage of the innate power of Phlogiston in order to allow ships to travel much faster than the speed of light. As such, a spelljamming journey even to the closest of unbreached crystal spheres would take centuries at least.

The Vast Unknown

While Voidspace may be mostly empty, there is more there to find than just the Phlogiston and Crystal Spheres. Small planets and meteors can be found dotted across the endless void, floating endlessly through space, rarely colliding with a phlogiston river and scattering a cloud of gas. Mysterious and powerful creatures wander through the edge of reality. Certain areas of space, known as The Weird, are warped and twisted by aberrant energy. Every journey on a spelljammer is an opportunity to discover something new about the cosmos.