The D'Vinnian Throne

This zone is a heroic instance found at the back of the royal wing of Crushbone Keep's upstairs (-59, 26, -42). 
A larger heroic dungeon with several nameds who have a chance to drop legendary and fabled items. You will need to kill watchful sentries to unlock most doors. This will lead you deeper into the dungeon. A decent description of which mobs to kill as well as how to reach the end of the instance can be inside the following quest in the Brell Serilis Timeline:
*Prospector of Lost Faith