Antharas Watchman Gilmore:
The abyssal jewel is guarded by cave keepers and cave maidens. Through their sorcery they have made the jewel invisible... As you kill them, the power of their sorcery will be diminished and the jewel will become visible once more.
You must destroy it and then find Antharas Watchman Theodric. He will give you a Portal Stone. You will find him at the entrance of the Lair of Antharas, in the deepest part of Dragon Valley.
If you plan to take any friends with you, send them to see me first. They will need Portal Stones as well.