You can only reach The Sundered Hall after you defeat Tylious on Master. The Sundered Hall is located directly under The Court of Cronia. Within it is Galeron Duskwither.
List of Sub-Zones: The Sundered Hall.[]
The Sundered Hall is only one room. However, at the end of the room is "The Grave" and a very odd structure... The zone smells heavily of vodka.