Citadel

"In the heart of this Forerunner structure, far above the troubled surface of the Ark, another battle rages."

- Bungie

Citadel is a Halo 3 map that was released on September 22, 2009 with Halo 3: ODST, as a part of the Mythic Map Pack. The Shotgun Spree achievement is attainable on this map. The map is a section of the structure first seen in the Halo 3 Multiplayer map Epitaph, which is a Forerunner "cathedral" that towers over the Ark.

Achievements
This map has a Skull for the Multiplayer Achievements. When found, it unlocks the achievement Citadel Skull, which is depicted by the skull and a Forerunner glyph on the forehead. The skull is near the blue side of the map; near the area where a doorway is in between two glowing "B"s. The skull is on top of the "B" on the right hand side. It is hidden atop of the B inside a small concealed place. Another achievement for Citadel is Pull, given to the player for getting a shotgun spree on the map, worth an overall 25 Gamerscore. A great way to get Pull is to play Action Sack and try to get 2Flag Shottys if lucky enough to get the game mode,pull the trigger when the crossairs turn red.

Trivia

 * It has been confirmed this map takes place in the same tower-like Forerunner structure as Epitaph.
 * The map was first designed to be much bigger and originally had an elevator for each team, though these features have been removed for undisclosed reasons, most likely to reduce possible lag or eliminate possible glitches associated with such features.
 * The map has a cross-shaped symbol similar to the symbols on Sandbox and Sandtrap.
 * Previously, the game developers mentioned the map being larger as well as featuring "elevators". The reason for this is that the map is actually an almost complete replica of the ground floor chambers of the "Shield Towers" from, The Covenant (Level). In addition, if elevators were present they would have most likely been located in the maps center on the platform much like it had been in the campaign level with the second level of the elevators being the "shield control rooms" like the ones seen in the campaign.
 * The strange roaring noises heard on Chiron TL-34, Assault on the Control Room and Two Betrayals can also be heard on this map.