Many of Khorvaire’s ghost stories begin in a small community on the edge of the Nightwood, an area thoroughly littered with Mabaran manifest zones. Over the millennia, all sorts of dark forces have spawned from or migrated to these gloomy woods: corpses there can naturally reanimate as zombies, wights use the manifest zones to bargain with the spirits of Mabar, and vampires have dwelled in the area since they first arrived from Aerenal. The wood’s proximity to Korth has prompted many escaped convicts to try to disappear into the woods rather than face the hangman; the lucky ones simply die, rather than becoming tortured creatures eternally reenacting their crimes upon the living.
Legends of the Nightwood suggest some kind of festering wound at its heart may be the source of its grim atmosphere. It’s possible that the region’s connection to undeath isn’t purely from Mabar, but is also due to a rift to the domain of Katashka or another overlord. Whatever the case, little is known about the region’s ancient history—the affliction the Nightwood suffers from may be the result of a long-forgotten conflict. Groups such as the Order of the Emerald Claw may wish to recreate this powerful undead influence elsewhere, but it may also be possible to undo the region’s cursed nature.
Despite the periodic risk of monsters, many people living on the edge of the woods have found its Mabaran connections to be valuable. Plants that survive growing in Mabaran zones have a wide variety of uses, from Jorasco disinfectants to magical waste disposal. Nightwood Ale relies on the area’s properties, and Seekers have numerous rituals that utilize its abundant necrotic energy.
A dense, shadowy forest that fills the land between the Karrn and Cyre rivers, the Nightwood is a forest with two aspects. The outer edge is a royal hunting preserve overrun with deer, foxes, and other small game. The deep woods—a tangle of ancient trees and deadfalls—is a dangerous, mysterious location into which few dare venture. Monsters and other foul creatures roam the heart of the Nightwood, sometimes slipping into the more benign regions and occasionally even out of the forest to threaten the farms and villages nearest the forest’s edge. Legends claim that a great chasm lies at the center of the Nightwood, an oozing pit that drops away to the depths of Khyber itself
Source: Eberron Campaign Setting
South of Atur and the Ashen Spires is the Nightwood. The forest’s fringes
serve as a hunting preserve, but not far inside, the woods become trackless,
filled with dark and terrible creatures. Some foresters claim that
burgeoning evil swells from an oozing wound at the wood’s center, a deep
chasm leading into the bowels of Khyber. Few can substantiate these
assertions, but the hideous things emerging from the shadows suggest some
truth to the rumors.
Source: Eberron Campaign Guide
This massive forest has close ties to the Plane of Mabar. Monsters sometimes slip out of the Nightwood to threaten the surrounding regions. Criminals and fugitives who flee into the Nightwood find the dangers within deadlier than any Karrnathi executioner.
Source: Rising from the Last War