Shadow World, or Kulthea, was one of Iron Crown's settings. There were 3 Ages:
The First Age was the era of the K'ta'viir, immortal humanoids who were masters of technology and magic. They self-destructed in a civil war - light vs dark - but remnants of that era are much sought-after. There are a few survivors, not all of whom are sane, and some have turned to evil. The major benevolent survivor is Andraax. The major evil survivor is Ondoval.
The planet, maybe the whole solar system, is prone to interdimensional instability. Various alignments, visits of comets, etc can open gates. One comet Saakain, is particularly associated with evil and the Unlife.
The Second Age started about 100K years after the end of the First and was a rebirth of civilisation. Various organisations came into being, both good and evil. Major players of note were the Loremasters, the Masters of Emer (a group of Titans), Lorgalis - an evil half-K'ta'viir - and Andraax. The gods made themselves known at this time. Again, it all ended in a big fight between good and evil.
The Third Age is the current age. Civilisation has arisen anew, and once again, things are shaping up for a showdown, what with the activities of the Secret Circle, the Priests Arnak, Dragonlords, and more.
Important to understanding Shadow World is that Evil is not necessarily tied to the Unlife. The Unlife goes way beyond Evil. Some of the Evil gods have ties to the Unlife, others do not. Andaras, the cat-god, comes to mind.
At one point, there was going to be an adventure path, a Grand Campaign, but that fizzled. Terry Amthor was a major player.
