Now that you are inside Andrew Station it is time for you to start making your way through it and to Eddie Winter's Bunker deep within it. Head on down the stairs in front of you to the first part of the subway. This part has 3 Raiders for you to deal with and an Attack Dog. Jump over the turnstill after you clear out some of the enemies to get at any survivors.
Past the Turnstill, head down the corridor to the East. There are 3 Frag Mines in this area so listen for the beeping and try to grab them as quickly as you can. Head down the stairs just past them after that.
Toward the base of the stairs you have Tin Can Chimes set up to alert anyone below of intruders. There is also a bathroom scale just to the right of the stair triggers some more traps if you are not careful. The far Western side has more Raiders for you to deal with. You can hack the nearby Terminal (Novice) to take control of the Spot Lights in the area. There are more Frag Mines on the tracks between the Eastern and Western sides of the platform.
As you cross over to the far side of the platform, be sure to use VATS to quickly find any mines in your path. There are 5-7 Raiders on the Western side of the platform. Most are toward the front but there are a few hiding behind crates and in the next shopping terminal. There is a chance that another Legendary Raider can be found in here. There is also a Machinegun Turret behind their front lines you will need to deal with to get around the corner and farther into the Subway tunnels. Having dealt with those Raiders and being on the Eastern side, turn to the North and start exploring the tunnels beyond.
Just inside the doorway is a Frag Mine so enter it carefully. At the far end of this hallway is another Machinegun Turret (Mark V) Try to snipe it from a distance or use a Pulse Grenade against it for a quick kill. Head out through either of the openings on the right after that and continue to the North.
Back in the Subway tunnels you will encounter more Raiders with more fortifications up around them. There are some in the nearby Subway cars so keep on guard for them. Most are going to be in the tunnel itself or in the small room just to the North of the Train Car.
Follow Nick to the North in the subway tunnel. Go through the first opening ahead in the Western wall. This leads to another hallway. Take the stairs there up. You then turn to the West. Just keep on following Nick as he winds his way through this corridor.
This will lead you to the entrance of the Bunker where Eddie Winter is. Just wait there for Valentine.