Pick up some Pickaxes (Kahah Hobichai in Al Zahbi (J-7) sells them). You will want a few because they can break very easily (up to eight in a row have broken, and bringing a stack of pickaxes is recommended).
Drop off a ledge North-West into a room with Aydeewa Diremites (they aggro level 75's - use Sneak to avoid aggro).
Immediately to the left (H-8), there's a steep ramp that leads south and down.
Go down the ramp to a room with leeches and a large pool in the center that looks like a Teleporter (H-9).
Note: This is the same room that is involved in the Blue Mage flag quest An Empty Vessel. If you are doing both quests at the same time, make sure you get the key item for this quest before starting the Blue Mage cutscene, as it will teleport you back to Whitegate automatically after the scene has finished.