Go see Bastien Milandra, located in the Beltigan Castle, with the Broken Ethereal Key, obtained through the Broken Ethereal Key quest.

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 between the spider cave and the green skraugs.

Reward:

• Ethereal Key