Worn by the nobles of the old bloodline that traces back to the forsaken Castle Cainhurst.
Found inside a chest in Cainhurst Castle. Enter Cainhurst Castle through the main door and head up the stairs and to the left. Enter the room on the right and the chest will be up against the adjacent wall to the right.
Arianna wears this kind of dress despite being a "woman of the night". This fact suggests she's a descendant of the Cainhurst bloodline.