From within the Empyrean, which some metaphysicists described as the præternatural aspect of the universe, the galaxy could be seen in compressed form, the stars bunched together and interwoven by the ætherial fires to form a breathtaking swirl of all colours of the spectrum that danced in circles like a whirlpool moving against a larger current. Call to Arms: Chapter I: "The Quæstor"
In Call to Arms, I decided to use a "hyperspace"-style method of faster than light travel. This ultimately took the form of "The Empyrean" which is essentially the spiritual world with "realspace" being the natural or physical world. I described it as præternatural rather than supernatural since the latter refers, in my mind, more to the Divine, being above nature. The Empyrean is not heaven -- it is inhabited by both the good and evil spiritual creatures.
One of the most important peculiarities of The Empyrean is that any natural creature that is exposed to it, or even looks at it through a view port, will go mad because their mind simply cannot handle that realm. The only exception to this is the Imperial Magistrates who can be safely exposed to the Empyrean, making them important as navigators as well as healers and leaders.
The way that everyone else gets around the Empyrean is by using charts created over the millennia by Magisteratal explorers. They plot a course through the Empyrean on their computer, then seal the ship tight; they then activate the Epulone generator which creates a field around the ship that drags it into the Empyrean. They then hold on for dear life as the computer guides the ship on the pre-calculated course and they hopefully emerge safely on the other side. Unfortunately, this is not nearly as reliable a mode of traversing the Empyrean as with a Magistrate, since there is no ability to avoid obstacles or take into account subtle changes in the "terrain". As a result, without Magistrates, ships face about a 2% chance of reappearing into realspace lightyears off course or not reappearing at all.
Such travels must also be done at a breakneck speed to avoid being attacked by the inhabitants of the Empyrean. Even Magistrate-guided ships must beware of these creatures, or at least the evilly-inclined or mindless ones, although these can be kept at bay by certain sacred chants being sung by Eternal Handmaidens of the Empire. The creatures of the Empyrean, especially ones of lower orders, cannot tolerate the sounds of these chants and will stay away from the ship (the Empyrean is not vacuum, and its æther is a superior sound conductor).