Hellfire Citadel is one of the new dungeons introduced with the Burning Crusade expansion pack. Introducing a newly popular system of dungeon making Hellfire Citadel possesses multiple "wings" and one large raid instance as well. This makes it suitable for nearly all players levels 60-70, each of the three total wings suiting a different level group and the final raid instance for guilds to attempt as well. Full of demonic orcs and a couple more nasty surprises Hellfire Citadel is quite the enjoyable dungeon. Located in Hellfire Peninsula, Outlands.

From the World of Warcraft Site:

On the blasted world of Outland near the Dark Portal stands the Hellfire Citadel, a nearly impenetrable bastion that served as the base of operations throughout the First and Second Wars. For years this gargantuan fortress was thought to be abandoned... until recently. This very much operation battle station has become inhabited by marauding bands of red, furious fel orcs.

Where this savage new breed came from is a mystery, but whats worse is that their numbers seem to be growing. Hellfire Citadel is the first new dungeon that players will encounter in Outland. It will consist of three complete dungeon wings designed for 5-man groups, as well as an exciting raid encounter.

The Hellfire Ramparts: 5-Players, Levels 60-62
The Bloodfurnace: 5-Players, Levels 61-63
The Shattered Halls: 5-Players, Level 70