Mass Fusion Building

(Note: To fully xplore the area and to reach the highest floor inside the building, you need a Power armor with Jet Pack, Jets (to slow time), and some Nuka-Cola Quantums (to restore AP). Tag the Nuka-Cola Quantum as a shortcut so you can easily use it while boosting)

Main Lobby

• Office room to the SW has an Advanced wall safe near the door way, sleeping bags, and a duffle bag.
• Security office to the NW has a Novice terminal which can be used to activate the two protectrons nearby. The terminal also has turret control.
• The elevator to reach the Main Reactor is located to the NE (accessible only during the related quest)
• Elevator to the SE to the fifth floor
• Ramp in the restroom to the SE leads to the upper floors. The second and third floors have minimal loot.

Main Reactor

(Accessible from the NE lobby elevator when the related quest is active)

• Prototype lab terminal to the SE can activate the protectron inside the room.
• Advanced Attendant's terminal can manipulate the security door, assaultron unit, and two laser turrets. You don't need to do anything anymore since the turrets and assaultron are all disabled, and the security door is already opened as well.
• There's a Hazmat Suit in the locker room to the SE
• Red steamer trunk in the middle west balcony, near the reactor window
• Small under the stairs to the middle-south has a Hazmat suit, novice Analyst's terminal, protectron pod, and Master Safe. The protectron and safe can be activated and opened using the terminal.
• Facilities Room to the north has two sentry bots, one is inactive and one will be activated once you grab the Berylium Agitator.
• There's a submerged steamer trunk to the NW of the reactor chamber. Look for the “Radioactive Materials” warning sign and dive in front of it.

4th floor

• Overdue book on the desk to the NW
• Advanced safe from the room filled with rubble to the middle-west.

5th floor

(Accessible via elevator from the lobby)

• Strength Bobblehead sitting on top of the wall statue overlooking the main lobby
• Room to the NW has a mini-nuke on the table and Master wall safe.
• Double-door to the north leads to the building's balcony outside. There's nothing in here so don't bother (unless you're planning to jump from outside)
• To reach the upper floor from the 5th floor, you need a Power armor with Jet Pack mod. You need to boost through the hole in the floor to the west side.
• Elevator to the NW leads to the 8th Floor or Glass Floor.

8th Floor/ Glass Floor

(This is the floor where the elevator stops during the quest Spoils of War or Mass Fusion and where you needed to restore Power)

• Head to the NW corner of this floor to find the Mass Fusion Labs Key and an Expert Developer's Terminal. The terminal has the option to restore Power. In the same floor, you'll also find an armor and weapon workbench.
• Beside the room with the circuit breaker is an Expert safe, half-buried in rubble.
• From the Glass floor, there's a ramp to the SE. Across that ramp is a computer near the window. There's an issue of Tesla Science there.

Several floors above the Glass floor, you'll find an open door to the middle-east that has a red steamer trunk inside. There are other explorable areas above and that's the tricky part in getting to. You need to reach the highest possible balcony (where the main elevator ends). And quicksave. You have to quicksave on your every progress so you don't have to work your way up should you fall.

Once you've reached the highest balcony, your objective is to reach the opening on the wall to the southern corner. Step on the railing and quicksave there; this will serve as your launch point. (This step requires several attempts and proper timing)

Now pop your jet, then boost to the corner. Boost once again towards that ledge, popping a Nuka-Cola Quantum mid-boost to replenish AP and prolong your jump. Aim for the corner so you can wedge yourself and give you temporary foothold while boosting up. Refer to the video below:

Once you reached that ledge, grab the Fusion Core from the desk then quicksave again. From there, you have to boost to the other corner to the north. You need to reach the next ledge above it, but it should be easier to reach compared to the first ledge. Once inside, unlock the Novice safe to get the pair of Freefall Leg Armor.