Secret Room On The Ark

On the level The Ark, there is a secret room right after the first cutscene. The room can only be accessed through Theater Mode. Right after the Pelican at the beginning lands, when the Master Chief begins to jump out of the Pelican, you may be able to see a glimpse of the room. To get inside, you need to fly up as high as you can against the mountain on the right side of the Pelican. Once you are against it, all you have to do is quickly tap the "Y" button twice. You will then be sent straight into the room where you are free to fly around. The true purposes of this room is currently unknown.

Video
This is a video showing how to get into the secret room: 300px

Possible Theories

 * The room has a door on the opposite side. The door is a Covenant door, which has blue lights on it. The blue lights indicate that the door is unlocked and can be opened if a player stands near it.
 * The room may have been part of the cutscene which took place at the end of Floodgate, acting as the stage. If one pays close attention to the cutscene, the details match to the Secret Room.
 * It could have been planned that you were going to fight in a Cruiser, but this part was cut at the end of the production and left there by mistake.
 * It could also be that Bungie first made the Covenant structure, then added the Flood Biomass, and left the structure there by mistake.
 * This room could have been a part of the first cutscene for the inside of the Covenant Battle Cruiser.
 * When fighting the Covenant early in the level with the ODST's, there are doors by the cave leading underground (although they are locked). Since the secret room is underground, those doors can quite possibly lead to that room.
 * Looks like a room in the level Cortana, but without Flood biomass.

Trivia

 * This room is identical to the bridge in the Cortana level, except the only difference the bridge has flood biomass.