Hub 3: Deathwind Chapel

''With the Heresiarch defeated, what treasures lie within his inner sanctum? To discover this, you must overcome forces with hearts as black as their former master.''

First and only visit
You appear in a small room with three doors and a portal back. Only one of the doors (the northern one) can be opened manually, the others will have to be opened via switches. Open the northern door. It leads into a room with a switch at the end - pull it and the western wall of the room will turn into a flight of stairs.