So how do I describe the appearance of being within the screaming vortex? It appears opaque from the outside. Are the stars obscured from within? Is it essentially a giant nebula covering many many light years? How would you describe the scene to your players as they orbit a star system (inside the vortex) and look through the viewports of their ship?

Whatever seems cool and appropriate?

Remember, it's supposed to be Dante's hell.

On a related note, how hard do you guys think navigation and piloting rolls should be in the Vortex?

Exoviper said:

Descriptions should be a mixture of the wondrous, the terrible and the impossible. These places are playgrounds of daemons and sorcerers… the physical limitations of reality need not apply.

The maps in the corebook (and parts of the description in the Screaming Vortex section of that book) deliberately avoid conventional concepts of navigation, and similarly descriptions of systems within the Screaming Vortex (or any other warp/space overlap area, like the Maelstrom or the Eye of Terror) should be similarly divorced from the realistic and conventional. The Warp invades the structured sanctity of realspace, and leaves it twisted and bizarre. Stars that bleed or which burn cold or shine with an impossible light in unknowable colours. Nebulae of smoke and congealed hate, and worlds made of glass and flesh and lightning.

Similar should apply to the planets themselves on the surface, especially as you go deeper towards the heart of the Vortex. Oceans of shrieking violet flame, wastelands of black sand punctuated by monoliths of energy-wreathed crystal, obsidian mountain peaks that pierce a sky of vermillion that flickers with black lightning, causeways of floating stone that sit amongst clouds pregnant with monsoons of acid or blood or greasy ichor.

I've also found the general rule of "whatever seems cool" is quite good way of describing the undescribable. First think of something normal, add something a little bit abnormal and then ramp it up to eleven. Things like planets with planets inside planets inside them, where people live and air smelling purple are all good ways of doing it.

One thing I have wondered is that how do you guys describe the transition to "warp travel" in the Vortex? Normally its going from normal space into a hellish realm, but when you are already inside a place that is partially inside the warp how does it differ? Do ships just activate their Geller fields (if they are sane/not powerful enough to actually need them, that is) and plough forwards or do they activate their warp drives?

Terraneux, I think that entirely depends on whether the ship is going along the vortex stream (so something along the spinny part of the maps) or going "through" the currents (from outside towards inside, which is generally near impossible). Also it depends on having an experienced witch-steersman, making the proper sacrifices, the favour of the Dark Gods, having maps, making deals with warp-dwellers for protection during passage, how close they are to the center and so on.

I think it would be a neat touch that if the PCs ever leave the Screaming Vortex for some reason, you casually mention that "You can't hear the screaming anymore."

In my mind, screaming is omni-present and constant in the Vortex, a shrill dirge of disembodied voices so pervasive that you simply don't mention it for the same reason you wouldn't mention the air. Everyone living in the Vortex has either gotten used to it or gone utterly, utterly insane.