The Tempest is a massive, roiling storm which permeates much of the Underworld. While nowhere near as powerful as a Great Maelstrom (or even a regular maelstrom), the Tempest is nonetheless deadly. Without knowledge of the proper Byways to travel, usage of the Argos Arcanos, or help from a Ferrymen guide, a wraith has no hope of making it through in one piece.
The Tempest does not consist of mere wind, clouds, and water, like the storms of the Skinlands. It is made of broken glass, magma, nightmares, acid, burning plasm, and any other horrific substance one can imagine. Also, unlike essentially two-dimensional storms which sit on an Earthly sea, the Tempest exists in three dimension; to most travellers passing through the Tempest, however, the storm appears to be two-dimensional.
The Shadowlands are "above" the Tempest and thus unaffected by them. Likewise, the Labyrinth and Oblivion itself are "beneath" the Tempest.
History
The Tempest is a fairly recent event: prior to the Third Great Maelstrom, the Tempest was a (relatively) sedate ocean called the Sea of Shadows. While each successive Maelstrom whipped up the Sea into a great storm, it always returned to its previous state. The Third Great Maelstrom changed this; the Sea remained in a constant state of disarray, and was renamed the Tempest.
Additionally, prior to the Third Great Maelstrom, traffic between the Shadowlands and the Underworld proper was much easier, but the Tempest cut Stygia off from the Shadowlands, similarly to how the Shroud cuts the Skinlands off from the Shadowlands.
Creatures
Without a doubt, one of the most common and infamous creatures found in the Tempest are the Spectres. Able to negotiate the fierce winds and horrific rains with little or no ill-effect, some Spectres prefer to bide their time in the Tempest, perhaps hunting for a stray wraith who has lost its way or causing difficulty for wraiths attempting to navigate through the vast storm. Shades in particular are fond of the Tempest, as that's the reason they became Spectres in the first place.
However, there are many other types of strange and mysterious creatures that make the Tempest their home. These creatures, sometimes called by their ancient name of Whistimmu, are many and varied in purpose and appearance. Some Doomslayers have attempted to catalogue the Whistimmu, but their ability to adapt to almost any condition the Tempest can produce has made this next-to-impossible.
Geography
Certain places in the Tempest are stable and safe for wraiths to dwell. Most prominent of these are the Dark Kingdoms and the Far Shores. Also of note are bodies of "water" which were once free of the Tempest's influence; while they are as chaotic as the rest, their location does not change. Among the more famous of these are the Sunless Sea, the Sea of Souls, and the aforementioned Sea of Shadows, as well as the legendary River of Death. The last, however, remains fairly stable even through the worst parts of the Tempest and is one of the most important Byways to and from Stygia.
Certain nihils are stable and appear or remain open in the same places time after time. The gateways to the Umbra are also consistant, although certain ones have fallen under the control of a Malfean.
Because of its turbulent nature, there are also several Shifting Zones in the Tempest; these are areas with strange conditions that drift through the Tempest that differ from the storm. Some bring pleasure and nice things, but most are areas of destruction and unpleasent sensations. Stumbling upon one is a one-in-a-million chance.
- WTO: Wraith: The Oblivion Second Edition, p. 36 , 276
- WTO: The Sea of Shadows, p. 23 -37