This V-shaped swampland is sunken in the center and cliffed along both coasts. This cupping causes water to form into standing pools and sluggish streams and flows. The resulting morass of water and vegetation is known as the Vast Swamp. The movement of water within it indicates that it generally drains southward. It must be that there are underground channels through which its outflow runs.

On a limestone bed, clays, silts, and peat from decaying vegetation have produced a rich carpeting. Fabulous lilies, creepers, and ferns throng among swamp cypresses in the tea-colored waters.

Lizard men and troglodytes compete for living space with the degenerate frog-folk, and all manner of poisonous toads, frogs, snakes, and insects add to the impressive range of unpleasant flora and fauna. These are said to be feral gray elves to the south, who are masters of vine-swinging above the virtually impassible swamp waters. There are many tales and legends concerning this area, especially in old times before the swamp was as extensive as it is now. The most oft-told one is that of the demilich Acererak, who is said to have ruled the swamp in the distant past and now has his burial place somewhere within its confines.

The cult of Wastri also calls the swamp its home, and a recent rise in undead sightings suggests that the necromantic order called the Bleak Academy may be stirring once more.

The folk of Sunndi to the north regard the Vast Swamp with ambivalence. It is a great protection against land assault from the Scarlet Brotherhood, but it is disease-ridden and packed with hazards such as will o'wisps and many monsters. The gigantic crocodiles of the central swamp grow fat on a diet of bullywug and grung, but the numbers of those batrachians are almost beyond counting.