The enemies that you encounter most frequently immediately after you show up on the scene in Hellfire Peninsula can be divided into two groups, the first being the demons of the Burning Legion, and the others being a hostile, savage line of orcs that seem to be coming from Hellfire Citadel in the center of the zone. After a few introductory quest chains, you receive the order to go into the Citadel to investigate. Hellfire Citadel is divided into four wings, and houses two Level 58-62 five-mans, one Level 70 five-man, and finally, a Level 70 raid for larger groups. The first of the entry-level dungeons is the Ramparts.
This wing is the wall of the Citadel, and your group navigates its way across, and eventually into the higher tower, which is where the Blood Furnace, the second dungeon is located. This dungeon was meant to get players' feet wet in the new expansion, and isn't much of a difficulty increase from the hardest Azeroth dungeons. The first boss you encounter is the wall's watchman, who has replaced his hands with large swords. He pulls with two healers, so he must either be completely obliterated before they can get a heal off, or controlled while your group takes down the healers, and then the boss.
After a short hallway, the wall splits into a Y-shape, and your group can go one of two ways, each route just a short walk from another boss. The first is a Burning Legion demon named Omor the Unscarred, who summons smaller demons who are pesky, but not too much trouble.
The other boss is named Vazruden the Herald, and he begins the encounter atop his dragon. When you pull him, he jumps down, and the dragon bombs you with fire from the air while you fight. After the orc has taken enough damage, the dragon will land and fight fair, so people need to be on their toes so that he doesn't run free and destroy your group.
The next portion of the Citadel, and a ramp-up in difficulty, is the Blood Furnace.
This is the indoor portion of the Citadel, and involves you going in and finding the source of the fel orcs power. You eventually discover that the orcs are holding a demonic pit lord hostage in their basement, and siphoning his blood to their forces to make them stronger.
The first boss in here is the Mo'Arg named The Maker. The Mo'Arg are a race of demon that are gifted in science and tinkering...so much so that they often rip out and off their pathetic biological parts, and upgrade them with machinery and weapons.
The next boss is a gigantic floating eye named Broggok. We don't know what it is, how it got here, or what its purpose is. Just kill it and take your things.Finally, you reach the center of the tower, and find a group of orcs performing some kind of restraining spell. The strongest is named Keli'dan the Breaker, and killing his minions causes him to break his concentration and attack you.
After you kill him, you are able to look through the grating of the floor, and see that the ritual that you interrupted was keeping the giant pit lord, Magtheridon, captive. Way to go!
The Level 70 Hellfire Citadel 5-man dungeon is called Shattered Halls. It is the home of the leader of the Fel Orcs in Outland, another sword-fisted fighter named Kargath Bladefist. Other nasty surprises in here include stealthed orc rogues that can kill your more fragile party members in one shot, and a trip through the sewer system.
The Level 70 raid in Hellfire Citadel calls for you to enter the base of the fortress and put an end to Magtheridon, now that someone was careless enough to release him. This is a one-boss raid, with only a small amount of trash leading up to it, similar to the way Onyxia was handled in the game's original vanilla release.
Those who are successful have the honor of impaling his head on a spike at their home base in Hellfire Peninsula.