How to Get Inside Dr Halsey’s Lab

You’ll need two players for this and you MUST play on Legendary. Skip to Rally Point Bravo on The Package. Play the level until Dr. Halsey announces her lab is open. Do not enter the lab or access the panel on the door to end the mission. If you don’t have a Jet Pack, grab one from the northern side of the lab entrance area. They are on the wall without any flashy Armor Ability holograms so they are a bit hard to spot.
One player must stay in a safe spot while the other accesses a secret panel. Fly to the far eastern line of buildings. Run up the ramp and turn left, or north. A fenced off area on the upper level lines the out-of-bounds region to the northeast. Drop off the northeastern corner and ease your way towards the rocky out-of-bounds area below but do not touch it! Hover above it and look for a panel with a green light you can access on a girder. Hit X to activate it.
This will open a door on the north side of the Halsey’s lab entrance. A half dozen Elites will stream out of here with Energy Swords. Fly over them or run a Ghost through them and enter the open door. You will then be transported to a hallway. Follow the hallway to the lab area where you can view a number of Easter Eggs, from readable data panels with inside jokes to old Halo art. Enjoy!