This quest is initiated by using a Rust Covered Key. This key has been known to drop on Fallen Crusaders in the Commonlands.
To advance this quest you must enter the Chamber of Suffering. The Chamber of Suffering requires is targeted at a single group of players and is located in the Ruins of Valmarr.
Useful information when you are inside includes:
Location of the Mausoleum: +416, -51, +362 Boss: A Decomposed Suitor is level 20 with 5 henchmen.