Mass Fusion Building

The Mass Fusion building is a location in the Commonwealth in 2287. This building is one of the Commonwealth's most recognizable landmarks due to its size and unique architectural design.

Roof
The rooftop is an exterior location and has it's own fast travel marker, the Mass Fusion executive suite. Although it is possible to get up there with clever use of the Jet pack or a Vertibird, it is normally accessible as part of the main quest endgame. The Mass Fusion executive ID that allows access to the elevator down will not be present if no relevant quest is active.

Above glass floor
This section is accessible from the roof by a quest locked elevator or at any time from downstairs if in possession of a Jet pack. The area is mostly destroyed offices where multiple caved in floors created one big interior space. This area will be abandoned if visited before being send there during Spoils of War or The Nuclear Option. During the quests, the Sole Survivor will be ambushed here by Synths or the Brotherhood of Steel as they exit the elevator.

Below Glass Floor
This area is the building lobby and some walkways and offices. Before any quest triggers, it serves as a normal game play location. It is casually accessible from the front door and the resident Gunners can be cleared out. When coming from above while on one of the relevant quests, the battle with the opposing main quest fraction will continue here.

Reactor Room
The reactor room is below ground level and is quest locked. The Beryllium agitator sought after by both the BOS and The Institute is located here. After dealing with the security, including turrets and Sentry bots, the agitator can be found in a large, highly radioactive central room.

Main building

 * Full set of possibly leveled power armor - Worn by the Gunner commander.
 * Strength bobblehead - On the head of the giant interior statue (accessible from the floor with the Gunner commander, powered elevator and exits to the Mass Fusion balcony).
 * Overdue books - On a desk on the fourth floor. One will have to go up to the fifth floor and go back down to reach it. Another is on a desk on the reactor level.
 * Mini nuke - On the same floor as the bobblehead in the room to the northwest where the Gunner commander comes out from.
 * Fusion core - On a desk 3 floors from the top, accessed through a destroyed wall facing the central shaft using the techniques described for the Freefall Legs.
 * Tesla Science Magazine issue #5 - On the computer bank, southeast mezzanine room, upper offices above the glass floor (on the same floor with the elevator after power is restored). The area can be accessed by using a jet pack to jump up a hole on the floor where the Gunner commander is and unlocking a door or by waiting for a late main quest to unlock the area.
 * Freefall Legs - In a safe in a small room near the top of the building's interior, in an area only accessible using the jet pack power armor mod, using the trash can wall climbing glitch.
 * Stealth Boy x 2 - One is on a metal shelf next to the chemistry station, three floors above the Strength bobblehead, at the same level with the glass floor. The other is in the same room as the Freefall Legs, on top of a small bookshelf.
 * Mass Fusion labs key - On the level with the glass floor in the northwest office room on a desk.
 * Executive key and ID card - in the desk within the executive suite. Accessible during Mass Fusion or Spoils of War.
 * Jack Rockford's log - In the intern's terminal in the same room as the Freefall Legs.

Reactor

 * The unique damaged hazmat suit can be found in a drawer right outside the decontamination room, that leads into the reactor room.
 * A hazmat suit can be found in the locker room behind the Attendant's terminal, sitting on a shelf of one of the lockers. And another next to the Analyst's terminal on top of a safe.
 * A sentry bot spawns behind the northern security door, which can be opened through the reactor security control terminal on the south side of the room before the reactor room. It has a fusion core. Alternatively, one can get the core and trip the security, the doors will then open automatically.

Appearances
The Mass Fusion building only appears in Fallout 4.

Bugs

 * The can chimes on the ground floor do not disappear after collecting them, however one can still get XP and tin cans for doing so.
 * Similarly the bathroom scale trap provides materials and XP upon disarming it, but the tesla trap will still go off.
 * Taking the large circular elevator from the lobby, back up to the Mass Fusion executive suite, sometimes causes the player to arrive in the wrong location in the exterior cell - a location which was not intended to be accessible.