This miscellaneous quest automatically starts about halfway through Ansilvund Excavation, when a room with a large fire pit with jagged edges in the center and a table on the left is entered. Just prior to entering, there is a trip wire that drops a macehead when activated. A voice will say: "I am Lu'ah Al-Skaven. Who are you to disrupt my work? Begone, or I will add you to my army of the dead!" The quest will then begin.
After obtaining the quest, keep venturing through the excavation site. Eventually, a large room with an animal puzzle to solve will be encountered. Pick up the book Of Fjori and Holgeir and read through it to figure out the puzzle combination. The solution is, looking at the animals from the lever: Eagle - Snake - Whale - Snake (from left to right). Near the book should also be Lu'ah's Journal, which will provide some insight into what she's doing there.
Continue through the burial chamber toward the final room, where Lu'ah Al-Skaven awaits. She will become hostile as soon as the room is entered, and summon multiple draugr and skeletons to attack. Once she is defeated, take the key from her corpse. The ghosts of Fjori and Holgeir will appear at the front of the room near the enchanting altar and thank the Dragonborn for freeing them from her spell.
As they disappear, the Ghostblade will appear next to the arcane enchanter nearby. Take it and go to the exit, which will be up the ramp to the right if facing the wall that the Ghostblade appeared against.
Continue through the room with the master-level chest. Unlock the gate and use the ramp to come to a ledge overlooking a frostbite spider and a draugr. Jump down from the ledge, then turn left to find the exit.