The Spiral Staircase is an odd, magical construct that in some ways seems to replicate 20 dimensional physics, including the creation and short life span of something akin to worm holes. Here is how the mages best describe it to those of us who have not had eight years of study in magical constructs: Imagine two spiral staircases. Each step on the staircase is a world. These two staircases are interwoven and spin in opposite directions. Because of this, as they spin, the different worlds will meet then separate. The worlds do not collide, but mesh together for short periods of time before drifting apart as the stairs continue to rotate. To a modern reader, it might better be seen as a double helix (like DNA), but with each strand spinning in different directions.
These examples are overly simplistic, because if it were this simple, then there would be an extremely limited number of worlds that would merge and then separate, when in fact there are at least hundreds of worlds that touch most other worlds. Some mages attempt to maintain the spiral stair analogy by saying that the staircases don’t rotate next to each other, but more as if they were formed in an “X” or cross, but not perpendicular to each other, more like 60 degrees to each other and therefore overlapping more extensively. Because this spiral stair metaphor is used so often, these interactions between the worlds are known as the Spiral Staircase.
When the worlds are “merging”, they do not merge in the sense of the two worlds coming together. Instead they merge in the sense that areas on the two worlds become gates or portals that allow people and animals to wander from one world to the other. Most often the differences in the worlds will make it immediately noticeable that you’ve moved to a different place, but sometimes the changes are subtle enough that people accidentally travel through without fully understanding what they did. While natural “full” gates do occur, most often it takes a powerful mage to breech the “skin” of the world and move from one world to the other. Natural gates are rare, while worlds moving close enough for mages to jump are far more likely, but still not common.
There are patterns to how the worlds interact, thus the belief that they are on a consistent spiral that continually comes around, though the patterns certainly do not indicate a simple spiral pattern or motion. (The mages would say that this is because we are thinking with three dimensional physics and not with the potential of magic.) In any case, gates (whether natural or magically made) are short term. Gates seldom last more than a few days or up to a couple of weeks. Once gone, anyone trapped on the other side will have to wait until the two worlds line up again. That could be a year, five years or vastly longer. (One known gate in the south of Drentae is thought to open every 500 years.)
The Spiral Stair has allowed non-native creatures and races to come to Fletnern. Some have come in sufficient numbers to be able to live here and multiply, but these are extremely rare. Most come over in small numbers, do some damage and then die off due to their limited breeding options. Worlds that merge with Fletnern more frequently are considered to be “close” to Fletnern on the Spiral Stair, while those that never form natural gates or more rarely are close enough for mages to breech are considered to be farther away on the staircase. Again, these are physical descriptions of magical constructs that do not need to make sense in our limited three dimensional ways.
Some of the worlds that are known to interact with Fletnern include:
Chong - A seemingly standard fantasy realm with humans, elves, dwarves and orcs, but the formerly enslaved orcs have rebelled and taken control of the world. Their Empire of Freedom, enslaves all humans under orc control.
Jorica - Jorica is a world where enchanting has been taken to an extreme degree and thus magic is plentiful and powerful. Though not blatant, the magic using “masters” do control the world, keeping extensive slave populations and preventing the freemen from rising in power. While Jorica’s enchantments work there, they do not work on Fletnern, so any mages who cross over often find themselves trapped because they must use only their own power to return.
Night and Day - On this world, creatures of the night (vampires, werewolves and other monsters) control the night, but humans, elves and dwarves control the day. Neither group is fully in power. The two forces live in a state of siege, seeing as they must defend themselves from the other side who will come to get them when their part of the day is in power with neither being able to win a decisive advantage.
Dragons’ Paradise - On Septocoxious, alchemy wielding dinosaur-like creatures created the six-limbed creatures from their own eggs (dragons as we would know them). In doing so, they were able to conquer their world. Now, the dragons, drakes and wyrm control the world, with some allies among the “beast-men” such as centaurs, satyrs, and minotaurs, but with far more combinations having been created than are known to most worlds (pig-men, wolf-centaurs, etc.). Each race has its job in the dragon regime, most of them acting as serfs to the dragon overlords, even the dinosaur men who created the dragons now suffer under their rule, though they suffer far less than the humans and dwarves do.