The Stormwall is metaphysical barrier between the worlds of the living and the dead in Orpheus.
The Creation of the Stormwall
Prior to Orpheus, the Stormwall was known as the Shroud. Late in the history of the restless dead, a relic nuclear bomb exploded in the Labyrinth, near the mouth of Oblivion. The result was catastrophic. Several ghosts were blown clear through the Shroud; many became stuck in objects, bodies, and other things in the Skinlands. But perhaps even more devastating than that, it started the Sixth Great Maelstrom, the most powerful storm of its type ever felt in the Shadowlands.
Thanks to the pressure of pretty much the rest of the Underworld crashing into it, the Shroud took on a lot of energy in a very short time. The energy became trapped inside the Shroud itself, thickening it and creating a strong, almost impenetrable barrier between the Shadowlands and the Skinlands. At this point, what the wraiths knew as the Shroud ceased to be and the Stormwall came into being.
The Dangers of the Stormwall
The Stormwall is extremely dense to the point that the Shadowlands can no longer be seen beneath it by those able to see the dead. It is full of the fury of Oblivion; howling winds rip through it, and unseen forces comparable to the Maelstrom slam into ghosts that try to get through it. However, like the Shroud, the actual thickness of the Stormwall in any given location depends on the vibrancy of life on the other side.
Because of its thickness and the hazards of navigating through it, ghosts in Orpheus, unlike those in Wraith, actually exist in the world of the living, albeit invisible and intangible to ordinary mortals. Only those who have experiences projecting, sensitives, and pigment abusers are able to see them alongside the living. However, certain ghosts have become aware of another realm on the otherside of the wall and have managed to cross it to investigate the history of the dead and to observe the Spectre armies of Grandmother and the Malfeans.
There are only a few ways to pass through the Stormwall, and all of the "safe" ones involve Horrors. These abilities are Banshee's Screaming Nothing, Haunter's Inhabit, Phantasm's Dream-Walker, Poltergeist's Rend and Rake, and Wisp's Storm-Wending. Inhabit and Dream-Walker, however, only allow a ghost to pass through when trying to leave the Shadowlands, and cannot be used to force entry. Spectral hives also cut through the Stormwall, but have their own set of hazards for regular spirits trying to use them as a passage. On very rare occasions, a nihil will open up in the thinner parts of the Stormwall, but this is not a dependable method for passing through.
Ironically, the creation of the thicker, fiercer Stormwall in place of the more sedate Shroud has made it easier for Grandmother to make her way into the world of the living, though the physics of why have yet to be discovered.