The Elder Scrolls IV: Oblivion Mod - Nuktan Huns Tomb 1.0

To learn about the quest you may stumble upon the cave by accident or you can read a copy of the Black Horse Courier in The First Edition or Cloud Ruler Temple East Wing. Once you read it you should be able to find the cave easier.

Once you reach the end, you will get the reward promised in the Black Horse Courier.