The first time this dungeon is visited you must have completed Parts 1, 2, and 3 already. Give Dmesne a Dazzling Shard and a Pyreal Bar. After this you only need to double click Dmesne to enter the dungeon. There is a shortcut portal located just West of Ayan Baqur at 60.3S 90.7W. There is a Black Marrow Reliquary inside on a 1 week timer. There are also SSK chests in fixed locations.