Go see Bastien Milandra , located in Beltigan Castle, equipped with the broken ethereal key , obtained via the quest for the broken ethereal key.
Say name, yes, work, yes, help, yes, seraphim, yes, ethereal key, and finally yes to Bastien Milandra .
He will then give you the ethereal key.
With this key, you will be able to access the ethereal zone, via the ethereal portal, moving in the zone between the spider cellar, and the green skraugs.
Gain: