The main feature of this floor is a hall of doors in the northeast corner. You'll find the Orichalcum just southwest of this hall. It is guarded by the most dangerous encounter in the dungeon, a group of Rhyos you should not take lightly. Prepare before the fight, though the best chance you have is to have Esuna at level 6 or higher to counter their Bad Breath attack. The door you're looking for is the second from the right. Inside you'll find the White Mask, unguarded, and a teleporter outside. Mission accomplished!