The Nightmare Forest is a haunted and dying forest. Is is said, only the people with the keenest magical awareness and strongest mental and magical defense can go into the forest, and still only for a short time, because it is said the forest is cursed with the darkest of black magic. This curse is said to make a person relieve their worst nightmares until it drives them to insanity.
The Knights of Greywar prevent letting any civilian come within 20 miles of that part of the forest, even those brave knights fear getting any closer than that and risk madness.
More information to come in time.