Darkhold once was the seat of a royal family and filled with knights. Now the keep is filled the rattling and moans of the undead and hisses of the fiends. In it's cellars a rift leads to a demiplane of negative energy.
The Tome of Andriaelle
Born of blue blood, her face as innocent as a newborn and her skin as pure as honey. No one would've suspected her to be the Lower Plane's chosen - a babe of iniquity, vileness and to be utterly irredeemable. Andriaelle.
Oft, whence the keep slept she would sneak out of her warm bed and while away to the darkness, the coldness beyond the castle wall, dragging with her a gagged street beggar or perhaps a harlot - One who would not be noticed or be cause for any concern should they vanish. Once out of earshot and prying eyes she'd purge her prey to the fullest and make great spectacle of it, painting it's lifeblood upon her own self with great decadence before feasting thereupon.
Many years of this passed and time would no longer conceal her deceit and deveilshness, for it burnt within her eyes - the promise of eternal and all-consuming damnation. And so it came to be that her wretched purity sprouted gnarled and wickedly horned-wings. Claws burst forth from her limbs and she sought to consume any and all. The keep walls became swatched in crimson, slippery and thick with the blood of the common folk and the keep's knights.
Many a blade too, had fallen upon her cursed breast but yield it would not. Magic faired little better save for it tickled her locks. And where 'ere she trod the scent of brimstone would be smelt, the flames would follow, and inexorably the blood would flow.
The voices of ten thousand tortured souls echoed from the flame cresent markings of Hell upon her vile self. To this day smatterings of such evil utterance can still be heard within the unhallowed halls of Darkhold! 
 The Tome of Andriaelle - In game plc