Quests:

The quests marked in Orange are the ones you must have BEFORE you enter the Instance for the first time. The rest are follow ups or quests you get inside the instance.

Both:

[53] Jammal`an the Prophet (Dungeon), given by the Atal`ai Exile, you can find him in the Hinterlands, Go to the southern part of ShadraAlor. Theres a broken-down temple and the exile is on a platform on the left as you face it.

[51] Into the Depths (Dungeon), given by Marvon Rivetseeker in Tanaris. You can find him in the middle of the desert, South of Gadgetzan. Before he gives you this quest you will need to go talk to Angelas Moonbreeze in Feralas (Alliance) or Witch Doctor Uzeri in Feralas (Horde). They will send you to talk to Marvon Rivetseeker. He will give you quest[51] The Stone Circle, you will have to go get a Stone Circle in Ratchet at the Workshop (left when walking off the docks), the stone circle is in a box on the floor, at the shop. Once you got it, go back to Marvon Rivetseeker, and he will give you the quest [51] Into the Depths.

[51] Secret of the Circle (Dungeon), you get this quest inside the instance, right after you complete [51] Into the Depths. It will be described in the walkthrough.

[53] The God Hakkar (Dungeon), given by Yeh`Kinya in Tanaris (Steamwheedle Port). This is part of a serie of quests, the initial one is given by Yeh`Kinya as well : [44] Screecher Spirits, the follow up is [47] The Prophecy of Mosharu (Elite). You will need a lvl 45+ group to do this quest(or less than that if you are lvl 50+) the tablets can be found on two named Trolls, Hydromancer Veltha and Theka the Martyr, inside the instance ZulFarrak. The follow up for that quest is [50] The Ancient Egg (Elite), the Egg is deep inside a cavern, on top of the temple of Jintha`Alor in the hinterlands. The mobs on the way up to the cavern are all elites, so go there with at least 2 or 3 lvl 50s (unless you are really higher level or really sneaky ). After you get the Ancient Egg, go back to Yeh`Kinya, and he will finally give you [53] The God Hakkar (Dungeon). This quest is a lot of work especially if you didnt do the first parts when it was of your level, but the final rewards are totally amazing for this level.

[55] The Essence of Eranikus (Dungeon), this quest is started by right-clicking an item you get when looting the the corpse of Shade of Eranikus, the final and hardest boss mob in the temple. This will be described later in the walkthrough.

Horde:

[50] The Temple of AtalHakkar (Dungeon), this quest starts with [43]Pool of Tears, given by Fel`Zerul in Stonard. You will have to gather Artifacts, you can easily find those underwater in the pool around the Sunken Temple entrance. Can be done solo. Then you will get the follow-up quest, you will have to go talk to the Atal`ai Exile, he will send you back to Fel`Zerul, and you will get the final quest: [50]The Temple of Atal`Hakkar. The Fetishes of Hakkar can be found on any Troll in the Sunken Temple. You will probably not finish this quest in one run, but you can come back and kill the Trolls outside of the instanced part of the Sunken Temple to get the last fetishes you need.

Alliance:

[50] Into The Temple of AtalHakkar (Dungeon), given by Brohann Caskbelly in Stormwind City. This quest is obtained after completing a long serie of quests, to start it you must first talk to Brohann Caskbelly, he will give you the quest [43] In search of the temple, youll just have to find the temple and enter it. Then go back to Brohann, he will give you [43] To The Hinterlands . You will go to Aerie Peak outpost in the Hinterlands and talk to Falstad Wildhammer, and then talk to Griffon Master Talonaxe, who will give you the quest [43] Rhapsody Shindigger, Rhapsody can be found east of Aerie Peak, talk to him and hell give you a quest. That quest will send you gathering items in Tanaris and Feralas. Once completed, go back to Rhapsody, he will tell you his tale and give you a tablet. Go back to Brohann Caskbelly in Stormwind, he will finally give you the quest [50] Into the Temple of Atal`Hakkar. The Atal`ai Tablet can be found anywhere inside the Sunken Temple.

Walkthrough

Group composition:

1. Tank Warrior or Prot spec Paladin
2. Healer Priest or Restoration Druid
3. Crowd Control Mage, Warlock, Rogue with improved Sap, or even a Shadow Priest (Shackle undead helps a bit here)
4. DPS or Utility class (Shaman/Paladin)
5. DPS

Where:

The entrance to the Temple of AtalHakkar is located in Swamp of Sorrows, in the southeast part of it. To reach the instance portal, follow the directions on the map below:

1. Secret of the Circle:

After entering the instance, go right. Go down the spiral stairs, then you will have a few pulls to deal with, and you will reach the Altar. Complete the quest [51] Into the Depths , you will get the follow up [51] Secret of the Circle. If you activate the altar, a serie of green lights will appear at different spots in the room, you have to memorize the order in which the lights appear, and reproduce it later on by activating statues on the upper floor of this room. If you have troubles with this part, check the following map, the order in which the Statues must be activated is shown:

Before activating the statues, you must first clear the pool down the stairs past the Altar. A boss mob will spawn there after you sucessfully click all the statues, so clear the pool.
At this point, you are probably wondering how the hell do you access those statues. Go back up the spiral stairs, and take the next path to the right (marked as to the 6 guardians on the first map). You will soon reach a room with 2 sets of stairs. One going up, the other going down. Go down! You will reach the Hall of Serpents. Clear your way through this Hall, and activate the Atal`ai statues one by one, in the order described in the above map.

After clicking a statue, a green light should appear. Once you have activated all 6 statues in the right order, an Idol will appear in the Pool, and also a mini-boss guarding it. Jump down at the Altar and prepare for the fight. The boss is pretty easy and straight forward.

After defeating it, you will have access to the Idol, go click it and you will be rewarded with 3 good items. Go back up to the entrance and take the way To the 6 Guardians of the force field. This time, take the stairs going UP.
2. The 6 guardians of the force field:

This area is kinda similar as the Hall of Serpents. You have to clear your way through a circle corridor, and the 6 guardians can be found in the side rooms. The pulls will be a mix of Humanoids and Undeads, so use Shackle Undead, Polymorph and Sap if you have that. Sometimes you will have to go down a flight of stairs to reach the nameds rooms. You can kill them in any order you like.
You can see them marked as green stars in the map below:

They are all quite easy to defeat but pay attention, some of them have annoying abilities. One of them especially, casts a totem, that spawns Skeletons every 2 seconds or so. Destroy that totem fast or you will end up swarmed. Besides this, they are really easy. Their names are: Zolo, Mijan, Hukku, Loro, Zul`Lor and Gasher. They mostly drop nothing, but very rarely drop green or blue items (5% chance) of low quality. So why kill them? You have to, for the simple reason that if you dont kill the 6 of them, there will be a force field preventing you from reaching Jammal`an the Prophet. Take also note that the Shade of Eranikus isnt targetable as long as Jammal`an is alive. So thats two very good reasons to kill them, no matter how worthless they are.
Once the 6 guardians are dead, the force field will vanish. Go back to the entrance, and take the leftmost way, marked as To Jammal`an the Prophet... etc.