Morrowind:Sixth House Base

Quick Walkthrough
# Receive orders from Caius in Balmora to wipe out a Sixth House base in Gnaar Mok.
# Visit Raesa Pullia in Buckmoth Legion Fort to receive a report of the scouting party.
# Travel to Gnaar Mok and talk to the locals to find the location of the Sixth House base.
# Enter the Ilunibi caverns and fight your way to the shrine.
# Fight and slay Dagoth Gares.
# Return to Caius.

Detailed Walkthrough
Orders from Caius
Once you have received copies of the lost prophecies from Nibani Maesa, return to Caius for your next assignment. He will warn you that the next assignment is very tough and advises you to make sure you're ready for it. Apparently, a Legion patrol stumbled across a Sixth House base near Gnaar Mok. Your orders are to find the base and kill the priest Dagoth Gares. Since Caius doesn't know the exact location of the base, you are to report to Raesa Pullia in Buckmoth Legion Fort.

Report from Raesa
Buckmoth Legion Fort is just south of Ald'ruhn and due north of Caldera. The quickest way to get there is to take a Silt Strider or Guild Guide to Ald'ruhn and then hike south to the fort. Raesa is just inside the main fort interior entrance. She gives you the report on the Sixth House base they discovered. Apparently, out of the original scouting party, only one person returned. He died shortly thereafter from the dreaded Corprus disease, but first mentioned a cavern on the coast named Ilunibi. Though Raesa is not familiar with it, she suggests asking the locals in Gnaar Mok about it. If you haven't been to Gnaar Mok yet, it's on the west coast of the island, southwest of Ald'ruhn. Raesa gives you directions to walk there, but the fastest method is to take the Ald'ruhn Silt Strider to Khuul, then take the local boat to Gnaar Mok.

Rumors in Gnaar Mok
Once you get to Gnaar Mok, talk to just about anyone to find out information on the Ilunibi cavern (you will need to raise their disposition to 50 or higher to get the information). You find out that the caverns are located on the north end of the island, on Khartag Point. You should have Khartag Point marked on your map when you ask about it, just a little northwest of the village. You should find the caverns named as Ilunibi, Carcass of the Saint.

Ilunibi Caverns
Just inside the entrance to Ilunibi you'll find a very nice little waterfall. It gets much worse just farther in, however.  Most of the monsters are random, but depend on your level: lower-level characters are most likely to encounter Skeletons, Ash Slaves, Ash Zombies and Scamps, higher-level characters more likely to have a chance of seeing Bonewalkers, Ash Ghouls, Ascended Sleepers, Atronachs and Golden Saints.  There's also a fair number of Dreamers around.

Once you get into the final section of the caverns, ''Soul's Rattle'', you should encounter Dagoth Gares, a unique Ash Ghoul.  He will initiate conversation with you and you should try and get as much information as you can before you exit: he can tell you some pretty interesting things about the history of Nerevar and Dagoth Ur, at least as seen from Dagoth's insane corrupted perspective. Once you exit the conversation he will immediately attack you. Gares is tough, casts spells, and hits pretty hard, but doesn't take too many big hits before he goes down. When he dies, however, he curses you with Corprus disease. After killing Gares, don't forget to loot the bell chamber nearby as it has some excellent loot (including the Fists of Randagulf).

At this point in the Main Quest you'll start seeing several barely dressed Dark Elves standing still on the roads. They call themselves Dreamers and are people who have fallen under the influence of Dagoth Ur's growing powers.  They're the same Dreamers that you may have already been seeing in other Sixth House caves and they will attack on sight.

Return to Caius
Once you've finished in the caverns, head back to Caius in Balmora (walk to Caldera, east of Gnaar Mok, and use a Guild Guide, or walk a little farther to Balmora southeast of Gnaar Mok - or simply cast Almsivi Intervention from the cave.)  Upon your return, you will be promoted to Traveller. Caius is concerned that you have corprus, but has been gathering some information of his own and has found someone who is doing research into Corprus Disease with a view to finding a cure: the Telvanni wizard, Divayth Fyr. He suggests you visit Fyr on the grounds that if he can't help you, nobody else can.

Bugs
 
  This can be fixed with the console commands   and  .
 

Quest Stages