Banshee Wetlands is a quest available after the quests of Termini Cliff have been completed. It can be done once the player has reached Lvl. 30 and unlocked Banshee Wetlands dungeon, although it may appear in the quest list before the dungeon is unlocked.
To complete the quest, Banshee Wetlands needs to be passed, that means the end boss needs to be defeated.
Click on [Campaign] -> Select the [Banshee Wetlands] -> Gain passage through the dungeon As you get close to Yaros, you discovered one of the most horrid areas of the Gaia continent, Fetid Swamp.