The Gurhai universe is not infinite. It is a geode: open space enclosed by an oval shell made of densely-packed organic and mineral detritus. There is a flat layer of sun systems that stretches length-wise in the very center of the shell. There are precisely one hundred worlds in the universe, separated into thirty-five sun systems; similarly, there are exactly one hundred sentient species in the universe, though not evenly distributed as one-per-world. All but two worlds in the universe are round and flat; Airdh (the First World) and Gurhai (the Last World) are the only spherical worlds, and they are at the far ends of the universe, a full year's travel apart. The suns are mobile and small, weaving or springing between planets in their systems, and there are no actual moons. In the top and bottom halves of the void, which are striated by the layer of worlds, there are creatures unlike any found on the worlds, living on the edges of atmosphere and gravity wells.
Gravitic ore is the glue that holds the universe together; it is a polarized mineral found at the center of a planet's crust. The polar side has a very strong attraction - gravity - and the non-polar side has a very weak attraction, but does not repel. Gravitic ore is dark and reflective, resembling a cross between hematite and coal anthracite. In addition to producing gravity, gravitic ore also produces the magical energy inherent in each world, similarly polarized; while the strength of gravity varies little between worlds, the magic density fluctuates greatly between planets, going from magic-dry to magic-rich. The polarity of the gravitic ore determines which face of a flat world will become the life-supporting side; the non-polar side will only be strong enough to keep very heavy objects in place, such as rocks and ore. The non-polar face of the world also contains dry ice, which creates the obscuring, drifting fog that obscures the undersides of the worlds. Gravitic ore can be carefully mined to be placed sparingly in the lowest decks of intersun ships, giving them gravity and a source of magic while they venture into the void between suns. Gravitic ore also constitutes the majority of the materials that comprise the shell of the universe, making it nigh-deadly to approach the rocky barrier; the intense gravity will pull any ships in and smash them against the rocks.
Sun systems fall into three distinct categories. All of the worlds spin on a horizontal axis, much like frisbees, but their arrangement in the system determines how the sun moves, when and how seasons change, and how long the night/day cycle is. Worlds spin much more slowly than the sun moves; it is the rate of the world's spin that produces the length of the seasons. (Note: Suns are spherical and do not possess gravity or magic, lacking the gravitic ore necessary to produce it. Suns are also considerably smaller than the worlds, with the largest sun being approximately a quarter of the size of the smallest world. Also, there are no moons, though some 3D objects of considerable size will get caught in a system's gravity weave and almost act as moons. However, these objects do not have gravitic ore, atmosphere, or life-forms.)
The first category of sun system only applies to the First and Last Worlds, the only two in the universe that are spherical; the worlds possess an encircling layer of gravitic ore whose non-polar side faces inwards, and the suns orbit them in a vertical circle while the worlds spin horizontally. Seasons change the most notably along the equator and are more constant at the north and south poles. Night and day are of relatively equal length, since the sun makes a full orbit of the planet each time it rotates once, and the sun appears to travel in a diagonal across the sky, rather than along E-W or N-S lines.
The second category applies to sun systems with two or three worlds. With two-world systems, the worlds face away from each other, and the sun swings an ellipse around them; for these planets, night and day are nearly equal. With three-world systems, the worlds still face away from each other so that the non-polar sides of their gravitic ore point inwards, and the sun circles the group on the outside; on these worlds, the night is twice as long as the day and can get colder. With these types of sun systems, the seasons are most extreme near the edges of the worlds, becoming more uniform and changeless towards the center of the planet. All second-category systems are horizontally aligned, so that the planets face outwards towards other systems and the sun's ellipse is horizontal.
The third category applies to sun systems with four or more worlds. In these systems, half the worlds face up and half the worlds face down in a rough circle; the sun is in the middle and springing up-and-down in a vertical path unendingly under the pull of the worlds' opposing gravities. Night and day is close to equal for worlds in this type of system. Seasonal changes are fairly predictable, since the worlds are spinning horizontally while the sun stays on the same vertical axis; seasons are more extreme near the edges of the worlds and taper into a seasonless temperate zone in the very center of the world.
The worlds, as previously mentioned, are mostly flat, round worlds. They support life, have gravity, and produce magical energy only on one face; the other face is rocky, barren, and clouded with mist from dry ice. Worlds vary greatly in magical density, but less so in size; the smallest world is half the diameter of the largest world, and all other worlds range between them. (The First and Last Worlds have a diameter equal to the largest world but, being spherical, have a far greater surface area.) The thickness of the world's crust is largely based on its size; since gravity is close to the same on all the worlds, smaller worlds have deeper crusts and wider worlds have thinner crusts, though some deviations from this pattern do exist. There is a rim of high mountains encircling the entire planet, which keeps creatures, water, and other resources from falling off the edge of the world. (If one managed to climb over the mountains, one could walk along the outside slope for a time, as gravity would pull one inwards as well as downwards - but after a certain point, one would walk past the layer of gravitic ore in the planet, past the polar side, and begin drifting away.) Atmosphere is generated by the plant life on each world; it has no defined boundary, but simply gets thinner and weaker as travelers move away from the world, becoming unbreathable eventually. The skies look different on each world; in many cases, one can see the other worlds of the system, if the world faces them; other worlds appear approximately as large as Earth's moon in the sky. Other suns within a few months' travel-time can be seen as bright stars in the sky, with the sunlit faces of any worlds from that system also visible as points of light. The worlds closest to the outer rim of the world-layer, and thus closest to the universe's shell, can see long-traveled light reflected off the surface of the densely-packed detritus, glittering faintly like the haze of a far-off galaxy (similar to how the Milky Way appears to us). For second-category sun systems, eclipses are common as other worlds in the system come between the first world and the moving sun.
Travel between the worlds is common. A dozen races design and build their own intersun ships, but the most common by far are Loi ships, halasshian ships, human ships, and buthinian ships. Human and halasshian ships have always had gravity and a source of magical energy, due to being constructed with a very thin layer of gravitic ore in the bottom deck, which also holds the soil, water, and plant life necessary to maintain a breathable atmosphere in the void. Buthinian ships do not have gravity or magic once they leave the planet; Loi ships were the same at first, but many Loi ships are now constructed with gravitic ore in a manner similar to halasshian and human ships. Because gravitic ore is responsible for generating magic, and because magic density varies so drastically between worlds, intersun ships constructed on magic-rich worlds are more prized by most than ships constructed on magic-dry worlds. Intersun ships are shaped and built much like water ships, complete with a keel, multiple deck layers, an outer/upper deck, and many sails. All ships have an entire deck or more devoted to flora; once the ship leaves the planet's atmosphere, all windows and doors are sealed, the upper deck is no longer walked, and the air produced by the plants on-ship keep the passengers alive until they reach the next planet. (In some cases, ships going between worlds in the same sun system don't need to seal up, if the worlds are close enough at that time that their atmospheres almost overlap. However, the thinner air can facilitate mistakes in judgment and navigation, so most ships seal up as a matter of course.) The universe is not an unbearably large place; fast ships can make the trip from the First World to the Last World in a year, with most sun systems having neighboring suns within a month or two of travel. It generally takes no more than a day to go between worlds in the same system, though a second-category system's interweaving sun can make navigation tricky. Intersun ships are generally very large; constructing them takes a great deal of resources and skill, and getting them off the planet and into the void is a one-time challenge once they are complete. Intersun ships do not land on-world once they have launched, since the world's gravity would smash the vessel into the planet; the people build docks well above the world's surface, where the pull of gravity is weaker, where the large ships can load and unload their passengers and cargo. Smaller boats without gravitic ore can make the trip between planet surface and intersun dock to transfer people and items. The hovering intersun docks are maintained via magical or mechanical means, depending on the world in question and the technology/magic level of the people who maintain the docks; the on-world boats that travel between dock and world are powered in the same fashion. Intersun ships themselves use a combination of magic, machinery, and void winds to move; the former two are what enable the ships to navigate within atmosphere or when close to worlds, but when between sun systems, the void winds propel the ships. Void winds are present everywhere near the layer of worlds in the universe, but they are not breathable by any world-dwelling creature; void winds are usually strong, can crop up into gale-force storms, and can occasionally die out and leave a ship idling in the darkness for a while.
The void is the entirety of the empty, unbreathable, unlit space between the shell of the universe and the layer of worlds. Since the layer of worlds is oval-shaped, like the shell, the outermost worlds come considerably close to the shell, with only a thin strip of void separating them from the detritus that marks the bounds of the universe. Due to this effect, the void is often considered to have top and bottom halves. The area immediately surrounding the layer of worlds is considered to be the innermost layer of the universe, and only here are void winds found; humans and many other races divide the rest of the void into ninety-nine spherical layers - like an onion, not a cake - and they call them hells. (Note: Most consider 99 hells to be the final number; however, some refer to the innermost layer as the first hell, bringing the total to 100 hells.) The outermost hells, closest to the shell of the universe, are filled with chunks of organic and mineral detritus that becomes the shell itself when sufficiently densely-packed. Most of the material that comprises the shell is reflective; long-ranging light from the distant suns glitters along the planes and edges, providing a kind of illumination in the blackness of the void. (Some theorize that there is light coming through from the other side of the shell, as well.) The vast amounts of gravitic ore present in the shell will smash anything of mass that approaches closely, but it also radiates immense amounts of magical energy. Like the atmosphere of the worlds, the pull of gravity and density of magic fades as one gets farther from the shell itself.
There are two kinds of creatures in the void: corporeal and semi-corporeal. Corporeal void creatures are often called dragons; their size ranges from a few dozen feet in length to such a size that a human could fit inside one's pupil. They do not communicate with any language or telepathy, and they are thought to be non-sentient, but they show a comprehension and intelligence that draws both those assumptions into question. There have been no documented cases of void dragons attacking intersun ships unprovoked; it isn't known what they eat or how they reproduce, and no wounded, visibly aged, or dead ones have ever been witnessed. Some smaller void dragons have been persuaded or coerced into service as living intersun ships, since they are easily ten times faster than the fastest manufactured ship; these steeds are reserved for the highest of causes and are almost exclusively serving powerful cultists or Lightworkers. Some tiny dragons also function as lifeboats to large intersun ships, transferring people and items from ship to world without needing a dock or an on-world boat. Dragons stay near the layer of worlds and do not venture into the depths of the actual void; they are also immune to gravity and are thought to be immune or highly resistent to magic.
Semi-corporeal void creatures are often called demons, and they do not go near the layer of worlds; they fill the spaces that the dragons do not. (Essentially, demons reside in the outer layers of the void - the hells.) Demons feed off magical energy, but since they don't approach the world layer, they must press close to the shell of the universe to feed at the fringes of the field of magic that its gravitic ore generates; they are semi-corporeal but still have enough mass to die if they wander close enough to be pulled in and crushed against the detritus. Many demons stay in the expanses of the void, away from both worlds and shell, and feed on other demons. Some demons, unlike dragons, can communicate with world-dwellers in some fashion, be it telepathy, body language, or verbal speech; they range an unmeasurable spectrum in regards to shape, composition (organic matter to ethereal energy ratio - some are entirely noncorporeal), magic preferences, intelligence, and disposition. Very small demons can be summoned from the void to the surface of a world by demonologists, though there are other, larger demons that stay in the void and remain either unknown or a thing of nightmares and visions. (The amount of magical energy on most worlds is far greater than that at the fringes of the universe's shell, so most demons are delighted to be in such a rich and populated area, since people tend to collect and condense magical energy within their own bodies. They are demonic Scooby Snacks.) The amount of magical energy needed to summon a demon is directly related to that demon's size and power, which is usually related to which hell that demon is from; it's almost impossible for one individual to summon a demon from beyond the twentieth hell. Strong demons cannot be summoned without dozens or hundreds of demonologists working in tandem - and since they'd probably all get killed in the process, no such attempt has been made. While demons only consume magical energy, their corporeal parts can be fashioned into or used as weaponry (teeth, claws, horns, hooves, blades, etc) to kill a physical body before consuming its magic. Completely incorporeal demons can possess inanimate bodies, or occasionally living bodies, in order to kill and eat. Some demons cooperate with their summoners, seeing it as a partnership wherein which they get good food and their summoners get living weapons; some demons fight any attempt at controlling them; and yet others are seemingly content to be slaves/pets to world-dwellers. The more magic a demon eats, the more powerful it is for a time, so frequently-summoned and -fed demons are quite hefty; most demonologists form a relationship with a singular demon and work with it to strengthen it and increase its usefulness.