As the new raid dungeon in the Wrath of the Lich King's tiered raid progression, Ulduar has remained undisturbed by mortals, far away from their concerns and struggles. Yet since its recent discovery, many have wondered what the structure's original purpose may have been. Some thought it a city built to herald the glory of its makers and others thought it a vault containing innumerable treasures, perhaps even relics of the mighty Titans themselves. Beyond Ulduar's gates lie no city, no treasure vault, and no final answer to the Titan's mysteries. All that awaits those who dare set foot in Ulduar is a horror even the Titans could not, would not destroy, an evil they merely contained.
   Many players have already gotten their Wrath of the Lich King raiding feet wet in Naxxramas and the Sartharion raid, but Ulduar is the first example of the expansion's much larger, truly epic scope of raiding, as will be evident from the moment you set foot in the instance. The new dungeon comprises two separate raid areas is the most obvious difference between Ulduar and its predecessors. One is that an epic battle against a vast army standing between you and the entrance of the dungeon proper in. another is that you'll dive into the heart of the dungeon itself and finally discover the secrets of Ulduar.
The new master of Ulduar has rallied a massive iron army to guard the entrance and prevent any unwanted guests including you from reaching the inner sanctum. Thankfully, you'll be able to face the Iron Army on even footing: a small fleet of siege vehicles will be on hand to aid you in the assault.
You and your friends will have to use these vehicles wisely to break through Ulduar's defenses. A mix of Choppers, Demolishers, and Siege Engines will be at your disposal, each granting unique abilities to the pilot and the passenger. Chopper drivers, for example, can create pools of liquid tar that snare opponents and can be set on fire by area effect attacks, while demolisher passengers can load themselves into the vehicle's catapult so that the pilot can launch them into the distance. If used judiciously, these and other abilities will help decimate the iron army and any other threats lying in wait between you and Ulduar.
 Ulduar illustrates the new design challenges and innovations that come with the bigger scope of this expansion's raids. In order to make raid content more accessible, a raid has to offer a lot of variety, but it also needs to include a very granular means for players to adjust the raid's difficulty. This concept was first realized in T with the introduction of Heroic mode, and Wrath of the Lich King is developing the idea even further with new hard modes.
Boss fights have a hard mode are affected by certain variables that players can control and that change the encounter's difficulty. For example, spread throughout Ulduar's vehicle section is four Defense Towers you can destroy. The more Towers you leave intact, the harder the encounter with the Flame Leviathan will be, but the loot will also be better.
Ulduar isn't the first dungeon to include hard mode, but it certainly makes the most use of it. Out of 14 bosses, 11 will have a hard mode that offers additional challenges and rewards. Ulduar will appeal to a wide range of play styles and the dungeon also has great longevity and high replay value.
   Ulduar is actually split up into two different sections. The first pits a group of players against a massive army that guards the gate to Ulduar's inner sanctum. Players will pilot a combination of Choppers, Demolishers and Siege Engines - each with unique abilities to defeat this massive force. Afterwards, they must face the Flame Leviathan, an enormous tank. The raid must weaken the Leviathan and then launch players onto the tank's back to sabotage it. After they've defeated the Leviathan, the raid can then precede on foot into the second section of Ulduar, which is more like the raid instances you're used to.