The Sahagin's Stash

Entering Sea Serpent Grotto from Yuhtunga Jungle, instead of keep turning right to go to Norg, just keep turning left until you reach N-14 on the map. At N-14, there's a hidden door, keep examine the door until the message change to "You see something silver glittering around the indentation." After you see this message, trade a Silver Beastcoin to the door to open it. After passing the door, go north along the right wall until you reach H-8. Drop down to the lower levels and keep going north along the right way wall -- you'll eventually reach the Sahagins' storage area. Examine the ??? at H-3 in the storage area to initiate a cut-scene and receive the key item: "Sea serpent statue". Go back to Norg and talk to Laisrean to finish the quest.

Note: I did this quest by switching to level 1 job and use Silent Oils and MGS my way to the storage area. Then I suicide back to my homepoint (which was Jeuno since I didn't want to set homepoint in Norg and get stuck there) and made my way back to Norg again. The reward is pretty nice, it's "blink" ninjitsu which sells for 100,000 gils in Jeuno.

Reward: Scroll of Utsusemi: Ichi
Prerequisite: Tenshodo fame
Repeatable: No
Title: Treasure-house Ransacker