This plane is featureless save for what has been built upon it. It is surrounded by a pale blue sky, but there is no warmth to it, though one can see. There is no wind, no waves, no motion here save what the denizens and occupants bring with them.
That isn’t exaggerating, either. The Nether realm is the source of Psychic emanations and powers , and Wraiths are feared in part so greatly because they cause psychic damage, not physical.
The Dreamscape is a dimension within the Shadow Realm, just as Nightmare is one in the Nether Realm.
Those in Perdition are always struggling to move, to travel, to explore, to venture. The great cities of Purgatory are overseen by a Power called the Lady Of Pain.
Perdition is said to be unpleasant, and the people there tend towards action over the apathy of Limbo.
Nightmare is as one expects – the place where nightmares are real, given flesh and blood and shape and form. All Nightmares comes from this Dimension. The denizens of Nightmare are in a war with those of the Dreamscape. Nightmare, after all, has every nightmarish being ever dreamed.
Nightmare, and the Shadows that inhabit it, are also engaged in a series of ongoing and fascinating battles with the assorted Mortal Reals, seeking a way to invade them. It began when they approached different people and made a bargain: Defend your dimension using your best warriors in single combat with the chosen of Nightmare. Now this ongoing series of mortal combats is held throughout different Mortal Realms.
It is said that Limbo is one of the seven great afterlives, and if so, it is a mighty boring one. Limbo is pretty much a reflection of all the most boring parts of life on Wyrlde. Nothing exciting ever happens here, it seems. People go to work, they come home, they do the same things over and over again, and the one thing that disrupts any of it is forgotten almost as fast as it happens.
That thing is Wraith attacks. They live on the souls of the people, and should a wraith kill you in Limbo, you are removed from the cycles and the Arenas.
It is often said that those whose horrors in life were filled with cruelty and loathing are tossed to Perdition in the hopes they will be taken to Purgatory. One does not seek to visit Purgatory. It is said that once there, the magic is so different from our own that you can become trapped there forever.