Getting to the Auchindoun is fairly easy unless you are too low a level, as the MOBS around it range up to level 65. It can be found in the large blasted bone waste area of Terokkar forest to the south of Shattrath City. You can also get access to it from the Alliance or Horde towns to the east and north east. They are the Allerian Stronghold and Stonebreaker Hold respectively. Auchindoun is the large ruins in the center of the bone wastes. When you reach there you have to head down through various tunnels to reach the bottom of the ruins, which is a circular plaza area. In the center is a meeting stone to summon other players and the instances can be found in tunnels around the outskirts of the central area. Another way to get to it is taking any of the stair ways around it up, and then wow gold finding a place to jump down through the ruins. There are several places where the ruins form long steps down, sure, you'll take some fall damage, but taken in steps, its fine.
The Sethekk Halls are the east instance around the Ring of Observance.
Quests There are two quests that are available to players, both from the NPC standing right outside the instance. They are:
Brother Against Bother - Kill Darkweaver Syth in the Sethekk halls, then free Lakka from captivity. Return to Isfar outside the Sethekk Halls when you've completed the rescue.
Darkweaver Syth is the first boss in the instance and Lakka can be found in a cage in Syth's room once you have defeated him. This quest gives a choice of very good necklaces upon completion and should be done.
Terokk's Legacy - Bring Terokk's Mask, Terokk's Quill, and the Saga of Terokk to Isfar outside the Sethekk Halls.
Terokk's mask is dropped by Darkweaver Syth, the Saga of Terokk is a book that can be found on the ground in the room just before Talon Lord Ikiss. The Talon Lord drops the last item, Terokk's Quill.