Spawns past the locked door. Placeholders are both the golems/geonids there (any) and the ones spawned off of traps. So bewarie. A Fabled may spawn on your head when you thought you were just rushing in to fight a grey.
Fortunately nothing in the zone sees SoS so you can send a rogue ahead to trigger the traps and see what surprises are in store for you before you get jumped.