Prequest starts at “Sharleedah’s Secret Document” as an item in your inventory.
To get “Sharleedah’s Secret Document” you have to kill “Sharleedah” in Aotulia Volcano.
 Sharleedah’s Secret Document
 Assault Plan
 Surprise Zurhidon
- This quest will also grant you access to the transport between:
- “Zurhidon-Commander” (52.33, 43.81) AND “Krasotimu” (33.15, 29.29).
- “Nao Sun” (32.61, 25.36) AND “Bacci Yamada” (28.37, 6.51).
Hall of the Demon Lord
Same prerequisite as Zurhidon Stronghold, but in addition you must have finished the instance Lair of the Demon Dragon and you must have used the item “Demon Dragon Heart Fragment”, which automatically drops in your inventory after killing “Gestero”.
sorry to say but your info is wrong you dont have to do any quest to get access to Zurhidon Stronghold or
Hall of the Demon Lord all you need to do is kill sharleedah get the secret documents accept the quest and RIGHT click the other two items you get and that will allow you into both of them (done it on over 20 chars) and as for gstero you only have to kill that if you dont want to die to get access to last boss in Hall of the Demon Lord