The Ring of Observance, located in the ruins of Auchindoun, offers instance portals in each of the four directions of the circle, and their difficulty ranges from Level 63 all the way to Level 70. The easiest instance of the four are the Auchindoun Crypts.
Here, a zealot renegade draenei cult is attempting to reanimate the corpses of the many draenei slaughtered during the Burning Crusade's invasion. During the dungeon, you fight back both the cult members, and the ghosts that they animate. They are led by the Exarch Maladaar.
The Mana Tombs are up next, and the ethereal members of the Consortium essentially 'hire' you to clean out the rival ethereals, who have invaded the Tombs and are pillaging the riches within for themselves.
Some of your adversaries include a giant voidwalker, an enormous stone giant...and an ethereal Prince.
Inside the Sethekk Halls, a rogue group of arrakoa have blindly followed their leader in search of the legendary hero of their race, Terokk, whom they believe has been resurrected.
Here, you face bosses like the Raven God, Anzu, whom on heroic difficulty has a chance to drop an item that allows you to ride him as a mount...and Talon King Ikiss, the leader of the Sethekk, who believes he has found the reincarnated Terokk...within himself.
The hardest of the four instances is the Shadow Labyrinth, which houses both assorted Burning Legion demons, and humanoid members of the mysterious Shadow Council cult.
The Shadow Council have summoned the ancient elemental, Murmur to serve them, but have been unable to control him. It's up to you to kill the Shadow Council responsible for Murmur's summoning, and then send him back where he came from.