Zul'Farrak is a Sandfury troll city located in northwestern Tanaris. Remember to pack your sunscreen, and get ready for a battle royale with the Sandfury Trolls. The level range is 42-46 after patch 2.3. Before the patch it was 42-48.

Location Sandsorrow Watch, Tanaris
Race Sandfury troll
End boss Chief Ukorz Sandscalp
Advised level 42-46
Minimum level 35
Player limit 5 (10)

Bosses:

Zerillis (rare)
Sandarr Dunereaver (rare)
Theka the Martyr
Antu'sul
Witch Doctor Zum'rah
Sandfury Executioner
Shadowpriest Sezz'ziz
Nekrum Gutchewer
Ruuzlu
Chief Ukorz Sandscalp
Dustwraith (rare)
Hydromancer Velratha
Gahz'rilla

History From Blizzard's Official World Dungeons site:

Troll legends tell of a powerful sword called Sul'thraze the Lasher, a weapon capable of instilling fear and weakness in even the most formidable of foes. Long ago, the weapon was split in half. However, rumors have circulated that the two halves may be found somewhere within Zul'Farrak's walls. Reports have also suggested that a band of mercenaries fleeing Gadgetzan wandered into the city and became trapped. Their fate remains unknown. But perhaps most disturbing of all are the hushed whispers of an ancient creature sleeping within a sacred pool at the city's heart - a mighty demigod who will wreak untold destruction upon any adventurer foolish enough to awaken him.