At one point in the life of your character you just might want to get into the Inner Sanctum, right? If this is true, please heed the following warning: You must have either the Inner Sanctum Knowledge or a Sealed Inner Sanctum Pass in order to enter the Inner Sanctum.
If you want to learna bit more about this dungeon, you best talk to Circe Levi inside Reet's Retreat. Beside Giving you some info on it's history, she also gives you a mission to find Fezael the Watcher.
One final word of warning: The Sealed Inner Sanctum Passes are temporary. They will be consumed upon use.
So the obvious question is this: How does one get either a Sealed Inner Sanctum Pass or the Inner Sanctum Knowledge?
How did I know you were going to ask? Well, mostly because it's not overly apparent how to get either one of these items. First, the Sealed Inner Sanctum Pass: You will need to get an Exarch Robe from the Temple of Three Winds.
Now that you have your Inner Sanctum Knowledge, pick it up and while holding the item right-click on the portal and your adventure will begin!
As soon as you enter, a strange voice will echo in your head: "Welcome to the Inner Sanctum, stranger. The Immortal One welcomes the Unbeliever with open arms." This room only has two portals, one leading back out (which will teleport you right outside of the Temple of Three Winds) and the other going into the first room of the Inner Sanctum. This is the best place for a team to meet and get ready for action. Once you're set, use the portal to enter the first room.
In the first room, you will notice that this dungeon is similar to the Temple of Three Winds in architecture, but of course the layout is much different. Here you will see groups of cultists and a few creepy undead with them.
Here is a map to help you out a bit:
The first group of cultists will be High Exarch Hannah (level 187), High Exarch Netole (level 187), Corrupted Soul (level 185) and Archdeacon Seemus (level 205).
The second group will be High Exarch Leonard (level 187), Corrupted Soul (level 185), High Exarch Niaf (level 187) and Archdeacon Tarrius (level 205).
The third group before the boss are High Exarch Izbel (level 187), Corrupted Soul (level 185), High Exarch Mellou (level 187) and Archdeacon Wynna (level 205).
At the far end of this long room is the main boss who will grant you access to the next room (as soon as you pound him into the ground). He will have two Corrupted Souls (level 185), one his left and right. Fezael the Watcher (level 225) will be a challenge to take on if you're there alone, however if you are level 210+ (obviously you would need the Shadowlands expansion for this to be the case) then you will have a good chance to solo him. Otherwise a team will be required not only for this room but the entire dungeon. Targeting this NPC will also complete mission you get from Circe Levi.
Note: You can save time by skipping combat with the cultist groups altogether, by running close to the right-side wall all the way to the end, it is very rare that you will get attacked doing this.
Once the boss is down, a portal will appear for a very short period of time, you need to right-click on it to be teleported to the second room.
As soon as you enter the second room be prepared for an ambush, because that is exactly what awaits you. 3 Corrupted Souls (level 185) and a Unhallowed Soul (level 205) will attack you as soon as you put your foot down. Once you deal with them you will see one of the cultists next to a portal. He is Elzek the Confessor, and under no circumstances should you try to attack him. He won't attack you, and he carries no valuable loot so don't waste your time with him. There is also portal right behind from where you appeared, and it will not send you back to the start of the first room. You should only use the portal if you have no other choice but to leave in a hurry, but be aware that if you're in a fight or a mob is engage in combat with you, the portal will not work until you are not in combat mode. This applies to all portals.
The good news in this room is that you can finally get a permanent key into the Inner Sanctum and access to the 3rd floor all at once, if you can manage to kill the two bosses here because each holds one half of the key. They are located on the west and east sections in this large area, the best tactic is to have a team in a specific spot for each side (images below). By luring (commonly known as pulling) a mob toward the team you can eliminate one mob at a time quickly. Once you have killed all mobs who may follow the boss when pulled, then you want to be ready for each boss.
The group on the east side will be a Corrupted Soul (level 185), Archdeacon Sisto (level 205), Archdeacon Treed (level 205), Preceptor Jjorick (level 215) and their main boss Iskop the Idolator (level 235).
Iskop the Idolator will be the toughest one in the room, for a few reasons. One is that like his counterpart on the other side he is able to summon Fanatics...and trust me they don't have that name without reason. A Fanatic will sacrifice himself about 40 seconds after he appears...and he will cause about 5,000 in health damage to all those around him because the explosion has an area of effect (AoE). Each fanatic must be dispatched quickly, or the team's chances of success will go downhill in a matter of seconds. Besides that, Iskop has two pets which appear to be from the Shadowlands, they are Pandemonium Idols that look like Hecklers and they pack a punch. You can either ignore them and focus on Iskop (I think this should be considered only if you have a good high level doctor) or have them rooted away from the team while you finish off the boss, because once he is dead the pets disappear.
The group on the west side will be a Corrupted Soul (level 185), Archdeacon Dreep (level 205), Archdeacon Jerid (level 205), Preceptor Andrew (level 215) and their main boss Jeuru the Defiler (level 235).
Jeuru the Defiler will be a bit easier to take down, but don't get too confident. Like Iskop he will summon Fanatics to his side (you know how to deal with that by now), but he will also blind you (which means all you'll see is darkness while you fight him) and weaken you temporarily by turning you into a skeleton.
Alright, combine the two halves of the key, and make it whole. Now you no longer need passes, and you can enter the last room of the dungeon. Go back to Elzek the Confessor and right-click your key on the portal to enter the third room.
Note: If you don't have a spare pass in case you die and want to get back, collect the High Exarch Robes and Archdeacon Robes because the Blind Cultist will give you a pass in exchange for one.
You will notice as soon as you're there that the last room is very similar to the boss room in the Temple of Three Winds where you face Aztur the Immortal. Actually, you will find his larger brother in this room, who makes Aztur look like a leet. Hezak the Immortal is gigantic to say the least. There is a portal right behind from where you appeared, and it will not send you back to the second room, but to the first one where Fezael the Watcher is. Only use the portal if you're done with the room or if you have no other choice (i.e. the only healer is dead and the team cannot survive the fight they're in), because then you would have to start from the very beginning. It's not as bad as it sounds because by then you will have a permanent key to the dungeon, but if there are too few in the first room the rest of the team may have to backtrack as well to open the portal to the second room.
There are two groups of cultists on the east and west sides, and the three toughest mobs on the north end. The layout of the room allows you to skip these groups if you choose, however if any of the mobs on the far north end are not pulled right...you could be facing a lot of upset cultists coming down on your team.
The group on the west will be Preceptor Brell (level 215), Unhallowed Soul (level 205), Preceptor Coshi (level 215) and Dominus Ummoh the Pedagogue (level 235).
All Dominus in this room cast AoE nukes, AoE DoT (damage over time), and they summon Fanatics and other pets, I highly recommend that the puller makes sure he only lures the bosses of the east and west sides to the team without any other mobs with a Dominus.
The small group on the far north will be Dominus Jiannu (level 235) who will be on the right side, the dragon Inobak the Gelid (level 237) will on on the left side and right between them an Unhallowed Soul (level 205) and Hezak the Immortal (level 245).
Now here is where you may want to start praying that nothing goes wrong, because it's going to be a hell of a fight to get to the main boss Hezak the Immortal.
The best way is to first pull the dragon Inobak, he will be the easier of the 3, but be sure that Hezak is looking the other way (to the right) so you're out of his LoS (Line Sight). Inobak does AoE (area of effect) nukes so get your doctor/healers ready for it, having an Meta-Physicist doing NSD would help in this fight. Next should be Dominus Jiannu which will have the same pattern as the other Dominus. Last but not least we have Hezak the Immortal, who is the toughest one you will face. Up to this point, a single team of level 200 could have done the job if they knew their profession well and were organized and prepared. However with the last boss only a single team of level 210+ would have a chance of success, otherwise you will need 2-3 teams of level 200 players (if they only have Classic AO installed).
Now that you have your team(s) ready for action, here comes the catch, yes there is a catch. Hezak the Immortal casts AoE nukes, AoE DoT (damage over time), and he summon Fanatics and other pets (Unhallowed Souls). He is very strong and he can kill pretty much anything in 2-3 hits, so having a doctor is a must. I would recommend having a doctor and another healer type like an Adventurer or a Martial Artist. This can be a long and tough battle, but if you are well prepared and everyone perform their task and know what they're doing you have a good chance of sending Hezak back to whatever pit of hell he comes from (well until he spawns again that is).