Head down the slope and over to the left of the ramp. The Eyebot, Sonya, will break down the wall nearby.
This leads to another chamber. Inside, on the right-hand side of the chamber, more Mirelurks will emerge from the water. The Mirelurk nest has more Mirelurk Hatchling. Be careful of the left-hand side of this chamber. There are a few radioactive barrels there and they can be somewhat intense (3-10 rads/sec).
You can also climb up on this Northern side to reach a Fusion Core that is above the radioactive barrels. Just head to the Northwestern side of the this ledge and jump up to the ledge above. Just head over to the machine and interact with it to claim the core.
This chamber is significantly more dangerous because a Mirelurk King can be found inside it. Be wary of its ranged blasts which do heavy damage. There can be a set of Power Armor found in this chamber, but it will likely be incomplete.
Head back to the previous chamber and go to the Northern wall from the pool of water in the middle of the room. Approach it and interact with the wall to bring Sonya over to it and blast it down. Follow the path as it turns to the East and into the next chamber.
Once again, you have some Mirelurks to deal with in this chamber. They are found just past the first wall in the chamber to the Southeast. The first nest to the South of where you enter has a number of Mirelurk Hatchlings that can erupt from it. Be on guard for them. Mix them with the adults and it can be very deadly for the Sole Survivor.
With the Mirelurks cleared out, head to the Northeastern wall. You will find a section of fragile wall. This is the part you will want to use Sonya to blast apart. This will take you to a much larger area, a subway tunnel.
Head into the main part of the Subway. You will encounter a number of Feral Ghouls that are rather determined to come after you. Continue to the North. There is a terminal to the left of the tracks which you can hack (Advanced). This lets you get at some Junk items. To progress you will want to to head through train car to the East. There are more Ghouls waiting for you on the other side.
Turn to the North and head through the hallway there. This leads to the subway tunnel beyond the train that you just passed through. Approach the wall at the Northern end and have Mel send Sonya after it.
There are likely to be a few feral ghouls on the other side of that wall. Be wary of them. Continue to the North from there. This leads to the next section of the train station. This chamber has another fragile wall on the Eastern side. Clear out the nearby Ghouls. After that, have Sonya blast the wall down.
On the other side is a control room. There is a locked Safe (Expert Level) to the left of the desks on the Eastern side. After that, open the door on the same side. This leads to a large room with more Ghouls inside it which are mostly on the lower level. There is one just past the first corner and two more on the Northern end of the area. It is multi-level but you are getting close to completing the dig itself. Throughout this area you will find destroyed Mr Handys. You can loot them for useful components of Junk. After that, take the ramp down to the lower level.
Go to the Northeastern corner of the room. Look at the Eastern wall to find the fragile part. Once again have Mel send Sonya to it. Time to head through another tunnel. Follow it to the South. This will bring you to the final room before you can go up into the destination itself.
The room you arrive in has a Chemistry Station if you have the supplies to create something here. You will need to access the local terminal to open the door to the final room though. This terminal is on the desk to the left of the Chemistry Station. Just opposite it is the door leading out.
There are more Feral Ghouls to be dealt with in this room. Try to stay on the upper level. If you do fall down, deal with the Ghouls then head to the Western side of the lower area. You will find a hackable terminal (Advanced) that you can crack. Inside you can find some ammunition cases. Head to the Northern side of the lower area to find a Ramp leading up. Take it and then continue to the North.
Once up the ramp, go through the hole in the Northern wall just past the top of it. Follow the short path to the next part of the room. This room has a fragile wall in the Southeast corner. Have Mel use Sonya on it to clear the way forward. This leads to the basement of the Strongroom.
There are numerous side passages throughout the area with lots of items scattered in them. It just takes some time to explore around to find them.
The Big Dig Quest
- Talk with Bobbi
- Meet Bobbi inside
- Join the dig
- Exterminate the Mirelurks 0/3
- Talk to Bobbi
- Meet Bobbi in Diamond City
- Get Mel Out of Jail
- Recruit Mel
- Dig to the Strongroom
- Meet with the gang in the strongroom basement
- Get out of the basement
- Enter the strongroom
- Side with Fahrenheit
- Kill Bobbi
- Talk to Fahrenheit
- Side with Bobbi
- Kill Fahrenheit and her men
- Open the Train car
- Get paid