From Halopedia, the Halo wiki
The Shutdown vacation is a glitch which can be performed on the Halo 4 campaign level Shutdown that allows the player to break the boundaries of the playable area and explore the map at will. This can be achieved by one player alone, but a second player is necessary if access to the open area containing the Didact's Cryptum is desired. This glitch can be performed on any difficulty, and requires that the Jetpack be equipped, and that the Cowbell and Tilt Skulls be activated
- Start the level at Rally Point Bravo.
- Proceed up the gravity lift.
- Acquire a Fuel Rod Gun from the Elite wielding it.
- Kill the Hunters that descend from the gravity lift.
- Once this is accomplished, start to melee to delay the checkpoint.
- Push the crate to the edge of the platform. Once it is in position, cease meeleing and load the checkpoint.
- Standing atop the crate, throw a grenade and shoot the ground with the Fuel Rod Gun to launch yourself into the air.
- Using the jetpack to maneuver, land on the edge of the gravity lift and proceed upwards.
- Exit the lift just before the end. Using the jetpack, fly to the platform landing with the HardLight bridge on it. Take care not to hit the trigger that will spawn the kill barriers and enemies.
- Get into the banshee and fly to the end of the room.
- Hover in front of the door. Exit your banshee, which causes the door to open, and then quickly re-enter it.
- Fly through the door, heading to either the left or right. Avoid the white square. Pass through the walls.
- You have now left the boundaries of the playable area. You are now free to explore the map at will.
- If you wish to access the large area at the end, it is necessary to have a second player play through the level normally after you circumvented the kill zones in the large area with the platforms.