This instance is the domain of Tseralith, the one responsible for the reanimation of the dead within Fallen Gate. Upon entry you are greeted with the ominous site of hallways lined with skulls of Tier'dal dragoons. Bats flutter about in the hallways and will respawn quickly, providing a nuisance as you make your way through the instance.
Find your way to the Keeper of the Chamber located at ( 58, -46, -92 ) /waypoint 58, -46, -92, who guards the door leading to Tseralith. He will offer Breaking the Seal to the Inner Sanctum, which is required to pass through the door. To complete the quest you must first locate the randomly chosen dragoon skull from one of the many that line the halls of the instance. Once you find the indicated skull, examine it and the correlated dragoon will spawn. Some examples of these monsters are: Dragoon B'Lavin, Dragoon Nezzka, and Dragoon N'Xry. Once you have done this three times, return to the Keeper of the Chamber who will become aggressive. Kill him and slip through the door right away. Important: Immediately enter the door once it opens. If you wait too long to enter (~10 seconds) the door will close and lock preventing completion of the instance.
Upon entry you realize why this places was sealed under so many lock and key. The horror Tseralith slowly forms in the middle of the chamber, with two servants at it's side. These two adds are worth AA and can be pulled separate from Tseralith. When you are ready, engage Tseralith and hopefully you possess enough skill to rid this forgotten section of Neriak of the horror that has plagued it for centuries.