|For the parent company, see Mass Fusion (company).|
The roof is an exterior location and has its own fast travel marker, the Mass Fusion executive suite. It is normally only 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, starting on the eighth floor, is accessible from the executive suite by a quest-locked elevator. The area is mostly comprised of destroyed offices, with multiple caved-in floors creating one large interior space. This area will be abandoned if visited before Spoils of War or Mass Fusion (by using a jet pack power armor mod to fly up from the lower floors). During these two quests, the Sole Survivor will be ambushed by synths or the Brotherhood of Steel as they exit the elevator.
Below glass floor
This area includes the building lobby and some walkways and offices. It is accessible from the front door, and is occupied by Gunners if encountered before Spoils of War or Mass Fusion. When approaching from above while on one of the relevant quests, the battle with the opposing main quest faction will continue here.
The reactor room is below ground level; the beryllium agitator sought by both the Brotherhood of Steel and the Institute is located here. After dealing with area security, including turrets and sentry bots, the agitator can be found in a large, highly radioactive central room.
- Overdue book - On the fourth floor, on a desk in the northern section; one will have to go up to the fifth floor then back down to the fourth floor to conveniently access this section.
- Strength bobblehead - On the fifth floor, on the head of the giant statue.
- Mini nuke - On the fifth floor, in the room to the northwest with the Gunner commander.
- Full set of power armor - On the fifth floor, worn by the Gunner commander.
- Mass Fusion labs key - On the eighth floor, on a desk in the northwest office.
- Two Stealth Boys - One is on the eighth floor, on a metal shelf next to the chemistry station. The other is in the same room as the Freefall Legs, on top of a small bookshelf.
- Tesla Science Magazine issue #5 - On the ninth floor, on a computer bank in the southeast.
- Fusion core - Five floors from the top in a small room through a destroyed wall to the south, on a desk. Only accessible using a jet pack.
- Freefall Legs - Three floors from the top in a small room through a destroyed wall to the east, inside a Novice-locked safe. Only accessible using a jet pack.
- Jack Rockford's log - In the same room as the Freefall Legs, in the intern's terminal. Only accessible using a jet pack.
- Mass Fusion executive ID and Mass Fusion executive lab password - In the executive suite, in the desk. Only present when a relevant quest is active.
- Oslow's office recording - In the executive suite, on the table next to the executive research lab terminal.
- Unique damaged hazmat suit - In a drawer right outside the decontamination room that leads into the reactor room.
- Two hazmat suits - One is in the locker room behind the attendant's terminal, sitting on a shelf of one of the lockers. The other is next to the analyst's terminal, on top of a safe.
- Fusion core - A sentry bot with the core spawns behind the northern security door, which can be opened through the Master-locked reactor security control terminal on the south side of the room before the reactor room. Alternatively, one can take the core and trip the security; the doors will then open automatically.
- Overdue book - On a desk.
- The Mass Fusion executive suite map marker is not discoverable before the related quests. As of patch version 1.9, the executive suite cannot be discovered until the quest the Nuclear Option reaches its conclusion.
- The executive suite is the highest point the Sole Survivor can reach in the entire Commonwealth, and offers an impressive view across the whole game world. Despite this, the Mass Fusion building is only the second-tallest structure in Fallout 4, after Trinity Tower.
- With careful timing and planning, it is possible to get a vertibird to land and drop the player character off on the executive suite roof, even before the related quests.
- One can leap from the southeastern corner of the executive suite roof and land safely in Goodneighbor without the use of power armor or Freefall Legs by aiming for the Old State House. The player character will be teleported to the main entrance of the settlement upon entering the cell.
- The building has multiple floors and many broken walkways. A jet pack makes navigating the facility much easier.
- With careful jumping, it is possible to reach the top of the building with a jet pack.
- If the player character glitches into the reactor room, the Mass Fusion quest will begin.
- The blue glow across the reactor room is likely the Cherenkov radiation effect. While mostly harmless by itself, it can only manifest this brightly in the presence of a very strong flow of particles, which would likely kill or fatally irradiate a human being the moment they are exposed to it, even in protective gear.
- There are two radiation hazards in the reactor room. One is a generic radiation hazard that causes 30 radiation damage (and 3 healing, if the player character has the Ghoulish perk). The second is a hazard specific to the Mass Fusion reactor which deals 153 radiation damage (and 15.3 healing with the perk).
- Swimming in the water in the reactor room will deal 50 radiation damage per second.
- Drinking the water in the reactor room will inflict 15 physical and 100,000 rad damage, killing the player character instantly unless they have the Lead Belly perk at its maximum level. Having the Ghoulish perk does not mitigate any of this damage. The Robes of Atom's Devoted from the Far Harbor add-on will protect from this damage; however, without the Lead Belly perk, radiation will still increase to a significant level.
- Touching the agitator receptacle or the blue beam emitting from it in the reactor room will inflict 1 million damage irrespective of any perks, instantly killing the player character.
- Hacking the Master-locked reactor security control terminal in the southeast corner of the reactor level allows the player character to open the security doors: one leads to impassable rubble, while the other opens the facilities room and reveals an inactive sentry bot.
- There is a steamer trunk in the reactor room underwater on the northwest wall, below a "Danger Radioactive Materials" sign.
- Each time the player character leaves the reactor room, they are decontaminated and lose all rads.
- If the player character did not support their faction in Mass Fusion or Spoils of War, the enemy faction will replace the Gunners and take over the building after the quest. On the other hand, the player character's faction will control the location if they are assisted. If Spoils of War is completed successfully, the Brotherhood of Steel will occupy the building. If Mass Fusion is completed successfully, synths will occupy the building for the Institute.
The Mass Fusion building appears only in Fallout 4.
- The can chimes on the first floor do not disappear after collecting them, and one can repeatedly obtain XP and tin cans for activating them again. [verified]
- The bathroom scale trap on the first floor provides XP and materials upon disarming it, but the Tesla trap will still be triggered even after disarming the scale. [verified]
-  Taking the large circular elevator from the lobby back up to the executive suite sometimes causes the player character to arrive in the wrong location in the exterior cell - a location which was not intended to be accessible. [verified]
- provisioners and their brahmin to appear on the executive suite roof, where they will be stranded and unable to leave. The only way to get them back to ground level is by using console commands, or somehow luring them over the edge of the building (since they cannot die, they will survive the fall).[verified] It is possible for
- If a companion is dismissed while on the executive suite roof, they will remain there until retrieved.[verified]