Fallout 4 created by Bethesda Game Studios.
Images used for educational purposes only.

- After an entry room and some stairs you’ll hear Synths ahead, one of which will rush the stairs if you make yourself known. Take it out, then find cover on the next floor and take out the remaining Synths. 

- The doors in the next rubble-strewn corridor are all locked, save for one at the far end and on your right. Pass through and you’ll find another hallway, this one blue-lit. Check the first room on your left to find a bunch of beds, boxes under each of the beds that are filled with items, and an Expert terminal set into the wall. Hacking the terminal allows you to deactivate all nearby Turrets. (It also says something about doors, but it won’t do anything for me. Shrug?) There’s another door in this room leading to a locker area, and a Novice locked door in here leads to a bunch of Pre-War Money and some Stimpaks.

- Back out into the hallway. There’s a junction ahead, and a Turret on the ceiling that you’ll have to wipe out if you didn’t turn it off. There are stairs on your left with another Turret, and probably a Synth if you make noise. Straight ahead is a door into a bathroom; there’s little of use. Take the stairs.

- On your right at the bottom of the stairs you’ll be facing another potential Turret, as well as more Synths. Grab a wall and gun ‘em down. Slip into the room on your next right. There’s a Fusion Core inside in a generator, and potentially more in an ammo box in the back. 

- Return to the hallway and head towards the wreckage you left behind; the hall turns left, and you’ll find rooms on your right and left. The right isn’t too interesting, but the left leads into a cafeteria, and from there a kitchen. There’s an Energy Weapons Bobblehead on a cart just inside the entrance, and a box with some explosives in the back room. Synths may pin you down in the cafeteria, so be ready for a fight.

- There are two doors at the end of the hallway. The one on the right, leading into an orange-lit maintenance / pump room, is a dead end - but you’ll find a Fort Hagen Armory Password in a toolbox at the rear of the room. The door on the left leads to another hallway, and you’ll see Synths strolling towards you if you’re stealthy. An explosive will do nicely here. Check a cart halfway down the hall for some meds.

- The hall ends at a security door that you can pop open via a nearby terminal, and that Password you just got, to find a bunch of supplies. The outer room contains a variety of meds; the caged area, protected by a Novice locked door, contains a bunch of weapons and ammo. Ever wanted a Fat Man and some Mini Nukes? You got ‘em.

- The next hallway has a door on your left and an open room at the end. The left room is a bedroom, and, among other things, contains a U.S. Covert Operations Manual, sitting beside the double bed. The Novice terminal in this room gives you another chance to deactivate Turrets. 

- The room at the end of the hall contains the last two Turrets, and past that is a door flanked by two American flags. Pop it open to find another bedroom. Have a look around - there’s a Novice locked ammo box by the bed with plenty of Fusion Cells inside - then approach the security door in the back. It’ll open on its own.

- Kellogg’s waiting in the next room, and despite what he says at first, you’re going to get into a fight.

Kellogg, one of the jerks who stole your kid in Fallout 4.
No Corn Flakes included.
Kellogg

Ouch. This fight isn’t so difficult because of its participants so much because you start in the middle of the room, and you’ve got Synths (and Kellogg) on both sides of you. This is painful enough for straight up fighters; stealth and ranged fighters with light armour are at a downright disadvantage. It doesn’t help that Kellogg has a solid gun, hurls grenades, and can use a Stealth Boy to disappear for about a minute. He’s much more likely to do this if you try to sneak attack his group. You have a few options:
  • Listen to Kellogg, then immediately turn and waste the Synth behind you. Wait for Kellogg to hurl his first explosive, get out of the way, get in cover, and start firing. Take out the second Synth, then go after Kellogg. If you brought a companion they can hopefully get his attention.
  • Listen to Kellogg, then try to cripple him immediately. The Synths are strong, but Kellogg is much tougher. Aim for his legs as soon as he’s done talking and try to get him on the ground. Taking away at least some of mobility makes him easier to kill. That done, back out of the room and go after the Synths.
  • Forget about the conversation and attack before entering the room. You can see one of the Synths through the stairs on your left, and a head shot can take it down. Once it’s gone you can take out the other. In this case Kellogg will almost certainly use his Stealth Boy to come at you invisibly, so be ready to watch for the telltale haze. Backing up through the previous offices and waiting for the effects to wear off is recommended. You can also drop Mines while doing this and lead him right into blowing his own legs off.
Regardless of the approach you take, you’ll probably have to fight this battles a few times before it turns out the way you want. Kellogg’s not only tough, he likes to pull out Stimpaks when things aren’t going his way. Quicksave before Kellogg and keep trying ’til he goes down.

- Even if you did talk to Kellogg, you won’t have every bit of information he can offer. Check his body for Kellogg’s Terminal Password, a Cybernetic Brain Augmenter (don’t forget this), Kellogg’s Pistol, and Kellogg’s Outfit, then look around. The room is full of items to grab, including a nice stash of stuff in a trunk on the right, but the main thing you want is a unique-looking terminal that’s also on the right. You can use it to get more info, as well as open the doors to this room. Grab the RobCo Fun magazine beside the terminal before you leave.

- Have a chat with Nick if you brought him along; otherwise, hunt him down and do the same. He’ll suggest you chat with Piper, back in Diamond City. Either way, you can find an open elevator back out in the hallway that’ll take you up to the roof. A terminal here will open the security door and let you leave. (You can also use it to disable the Turrets outside Fort Hagen if you haven’t already.) On the roof you’ll see something quite epic, and you’ll receive the Shadow of Steel quest.

- Head back to Diamond City, or wherever you’ve stashed Piper. Nick will be waiting, and he’ll chat with you and Piper over what you’ve found. Point out that you have the Cybernetic Brain Augmenter and you’ll start the next quest, Dangerous Minds, and have the option to head to your next destination with Nick, Piper, or neither.