[Sellas] Voyage to the Bottom
Start it with Shubert in The Final Edge of Light 6. Complete it with Shubert in The Jellyfish.
Requirements
Lv. 240+
Quests
NPCs
Locations
Shubert Start
Shubert Complete
Connected quests
Dialogue
Turning in the quest
Additional replies
There's almost no problem you can't solve by defeating 100 monsters.