Coilfang Reservoir is a new dungeon in The Burning Crusade expansion somewhat reminiscent of Blackfathom Deeps. Also, Coilfang Reservoir is somewhat similar to Hellfire Citadel in that it contains 3 5-man "wing" dungeons, Slave Pens, Underbog, and Steamvault, as well as one 25-man raid dungeon, Serpentshrine Cavern. The new home of a growing army of Naga and various other water affiliated beasties Coilfang Reservoir is located within the Zangamarsh in Outlands.

From the World of Warcraft Site:

For thousands of years, the draenei have been interring their dead in Auchindoun, their most sacred temple. However, it was infiltrated by agents of the Shadow Council bent on summoning a horrifying creature of immense evil. Their vile act of magic resulted in a massive explosion that blew the temple apart and reduced the surrounding area into a charred wasteland.

The blast also caused a rift in the Nether itself, drawing the otherworldly Ethereals into Outland. The interred draenei now walk the ruins as restless spirits. Meanwhile, the horrific entity summoned by the Shadow Council threatens to overwhelm their efforts to contain it. You must prevent this evil from being unleashed upon an unsuspecting world. Auchindoun is divided into four wings, and is designed for a party of five characters levels 64-70.

Mana-Tombs: Levels 64-66
Auchenai Crypts : Levels 65-67
Sethekk Halls : Levels 67-69
Shadow Laybrinth: Level 70