By User Eldersphinx
Every elemental plane has its pockets of imperfection. Places that are less pure - and more interesting - than raw elemental material or unrestrained energies. The plane of Vacuum, for all that it's defined as elemental absence of anything, is no exception. The stable collections of outside matter are rarer, true; the nature of Vacuum is to slowly erode, demolish and disperse anything it comes in contact with, and preventing this is not straightforward. Still, they exist, and are prime sites for adventure.
Of the types of landmarks found in Vacuum, these are the most comprehensible to mortals - and with good reason, since mortals are generally responsible for creating them. A redoubt begins when someone brings a large quantity of outside matter into Vacuum... and persists when someone realizes the degree of constant effort required to keep said matter intact and compact in the face of Vacuum's depredations, and devises a plan to do so.
Redoubts can take many forms, from the citadels of Vecna and the Doomguard to the hollow cinder cities of the Abduldinach efreeti to the spindle of frozen lightning conjured by the aasimon Matariel. All redoubts, though, are ultimately defined by the measures taken by their residents to hold back the emptiness beyond their borders. The simplest such method is use of spells - which must be powerful, varied, and ceaselessly renewed. Conjurations to feed the encroaching Vacuum, or evocations and transmutations that can compact and restrain the redoubt's foundations, are the most commonly used tools here. No redoubt can last for long with only a single engineer to maintain it, though, and yet groups of spellcasters fare little better given the chance of envy and internal discord. To try to keep a redoubt strong with merely mortal tools is a difficult proposition.
Other means exist, of course. More than one redoubt has been built around a caged artifact, a chunk of comatose godstuff stolen away from Anubis, a source of some primal Positive energy, or yet weirder means. The Convent of Unwhispered Secrets, for instance, is said to have as its foundation stone the seed of an entire unborn Prime Plane, and so pushes back Vacuum's consumptive influence. Even these greater means, though, require directive attention to function properly, and can be breached if managed incompetently or left unattended. When its protection fails, the redoubt's outer workings are quickly stripped away, leaving only a tangled remnant of material surrounding the quiscient power source. Moreover, anything powerful enough to maintain a redoubt is also powerful enough to serve other ends, and is at risk of being seized or stolen by those who seek to shape the wider multiverse. If this happens, the redoubt collapses upon itself, and its wreckage eventually erodes away into Vacuum once more.
In the long run, simply put, no redoubt can hope to survive. They are strictly temporary things, often outlasting the life of a human or even an entire ruling dynasty, but eventually doomed to disaster of one kind or another. Once breached or abandoned, a redoubt generally suffers irreparable damage, and eventually disperses to nothingness.
Not all Vacuum is created equal. While large parts of the plane of Vacuum are merely passive, empty spaces that simply remain unfilled by the nature of their home plane, there are areas where reified nothingness is far fiercer, pulverizing and eventually annihilating anything that gets too close. And yet, like hurricanes that have an eye of calm at their centers and suns whose cores burn less fiercely than their coronas, there are places where Vacuum becomes so destructive that it forms a repulsive shell around an area of placid stability. The interior of these areas are called Hollowings, and they can - with proper care and preparation - be quite comfortable places to live.
The first challenge with regards to exploiting a Hollowing is simply finding one. By their very nature, they are in parts of the plane of Vacuum that are not exactly safe to traverse, requiring substantial magical protection. What's more, they are effectively invisible, even to most magical means - until one is actually inside a Hollowing, it merely appears to be an especially volatile area of Vacuum. One favored means of detection is to use native wildlife as trackers - experts within the Doomguard, for instance, have taken to breeding ghostwings, albino batlike creatures able to shriek and listen through Vacuum itself. (It's rumored that the Mercykillers have begun a project to acquire their own ghostwings, to use in tracking escaped criminals who've fled to the quasiplane... something that the Doomguard have not taken too kindly to.)
Once a Hollowing has been located, there's still the task of getting inside. Teleportation and plane-shifting magic work, of course; for large inanimate cargoes and the magic-averse, an alternate means of entry is to construct or conjure a protective casing of some tough but disposable material, and physically push it through the Hollowing's destructive shell. It's important to note, though, that this trick only works for getting in. When approached from within, the shell of a Hollowing behaves much differently - it exerts a mild repulsive effect that's enough to keep gases encaptured, but any object that has sufficient momentum to overcome the repulsion and make contact with a Hollowing's shell from inside will find itself instantly disintegrated. (A living creature thrown against the inner shell of a Hollowing should get a save vs. Wands to avoid contact. Failure means that a wish is needed just to get enough of a body back to raise from the dead.)
The last trick with a Hollowing is keeping it in balance, long-term. The interior of a Hollowing is absolutely a closed system - nothing gets in except through deliberate action, and nothing leaves unless deliberately removed or destroyed. Left unattended for too long, a Hollowing's air will foul and its interior will overheat. Even if these are controlled for, a Hollowing can be overrun by vermin, run out of food or other raw materials and be abandoned, or suffer a magical catastrophe that makes its environment impossible to maintain. Hollowings that have become uninhabitable in this way can make for... interesting reclamation projects, with potential threats ranging from environmental hazards to leftover magical traps to Vacuum natives that have somehow found a way inside to Prime vermin that have adapted to their new home.
III. FROZEN STARS
Over the infinite history of the multiverse, many attempts have been made by natives of other planes to transform Vacuum, or find some way of filling it with hospitable outside matter. None have been perfectly successful, but some have come close in their own way. One such effort, a twisting and collapsing of Vacuum itself by some long-forgotten Prime civilization, alters the space of the plane in such a way that outside matter is not simply destroyed, but instead dragged inexorably towards an infinitely small central point. These anomalies are known as frozen stars.
Not all frozen stars are equally useful. Some are small and weak, their influence only partially offsetting Vacuum's destructive influence; they are useless except as landmarks. Others are too powerful, able to suction in any matter that comes close and compact it down to nothingness in a matter of moments. Between the two extremes, though, are specimens that can actually preserve outside matter for a nontrivial span of time, and these frozen stars often have a corona of solid mass, atmosphere and sometimes even inhabitants.
Living around a frozen star is often chaotic if not outright dangerous. While it's entirely possible for air, heat, solid ground, drinkable liquid and the other necessities of life to all be trapped within a frozen star's ambit, there's no guarantee that they'll be arranged in any sort of accessible manner, or even continue to stay in the same place from day to day. Waking up to discover that the resevoir pond's drained off, or that the atmosphere's only filling half the space it used to, are uncommon but not unheard of events near a frozen star.
One special longer-term hazard is the possibility of being bodily altered by the frozen star - having one's physical form compacted in on itself. In game terms, the character gains a bonus to Strength (denser muscles), but a penalty to Constitution (skeletal stress and organ rearrangement) and to all saving throws (strain on the nervous system and limbic disorientation). In addition, the DM may choose to call for a system shock roll at each time interval after 1 week. The Strength bonus and saving throw penalty are lost once a character departs the frozen star, but the Constitution penalty remains until magically healed (usually involving regeneration or similarly potent effects). Also note that the time intervals below are averages; for a particular frozen star, they can be anywhere from half as long (if the frozen star is particularly powerful) to three times as long (for weak or erratic frozen stars).
Time Interval Size Chg Modifier
12 hours x0.99 none
36 hours x0.97 none
3 days x0.94 +/- 1
1 week x0.9 +/- 2
2 weeks x0.85 +/- 3
1 month x0.8 +/- 4
3 months x0.75 +/- 5
1 year x0.7 +/- 6
5 years x0.6 +/- 7
25 years x0.45 +/- 8
150 years x0.25 +/- 9
The final risk involved in visiting a frozen star involves departing one. The seemingly most straightforward method, teleportation, is risky; something in the frozen star's structure tends to disrupt such magics. Anyone attempting to teleport away from a frozen star must save vs. spells; on a failure, the teleportation effect fails, and the subject instantly adds their character level in days to the actual length of their stay for determining the frozen star's effect on their body (as per the chart above). Even if the save succeeds, chances of a botched teleport are doubled (roll twice, take the least favorable of the two rolls). Plane shifting is somewhat more reliable, in that it will always allow for the caster's departure; however, a save vs. spells is still required, and on a failure the destination of the plane shift is off-target (DM's exact discretion as to where the traveler ends up). The simplest and safest way to escape a frozen star involves use of the reverse gravity spell - being careful, of course, to cast it in a place where no barriers can interfere with the caster's departure. Failing that, natural or magical flight at a speed of at least 72" is sufficient (which likely involves some combination of haste magic and custom spell research).