Aharunartus is one of the caves located in The Elder Scrolls III: Morrowind at the Bitter Coast. You can get here by going west from Seyda Neen or south and a little bit southeast from Hla Oad.
There are four slavers here, all of them low-level. Brothes Oran is a trainer, but he is hostile. There are also four slaves behind a locked gate.
Most of the loot is random, but Yatur gro-Shak is carrying a copy of the Medium Armor skill book Bone, Book I.
The slave key can be hard to find since it's not on any of the NPCs. It is lying on top of a locked ancient chest in the cave near Yatur gro-Shak.