The entrance area is a destroyed facility full of mirelurks and mirelurk hatchlings, along with dead raiders. In the center of the building is a large atrium with a hole in the middle that leads down into the partially flooded basement area. Drop down into the hole and one will see a pair of locked doors as well as a hallway off to the side. The hallway leads into a few rooms full of shelving and radioactive barrels, then eventually to a room with a fusion generator and a terminal. Activate the door locks via the terminal and the locked doors across the cavern will open. When dropping back down to the central area with the pool of water (or throw a grenade into the pool), a mirelurk queen will emerge. Before dropping down, grab the fusion core out of the generator.
Through the doors is a room full of radiation and then a hallway. The right hall leads to a room with another terminal, while the left leads to a room with frag mines and a safe, then a raider base. Note that the left hall also spawns a unique mirelurk encounter, with the mirelurk busting up the floor until finally emerging at the end of the hall. Continuing past the room with the mines and safe, there is a ramp leading up into the raider base. The base consists of several floors with a raider in power armor in a room near the top. The key to the locked Master door can be found in a metal box in the enclosed area behind the turret (around the corner from where the door is located).
Through the locked door is a room containing one or more raiders, as well as a sniper rifle and some ammo. The hole in the wall leads to a walkway above the statehouse atrium with the hole down into the sewers. Across the walkway is a room with one or two raiders, a turret, a steamer trunk, and an attack dog. One of the raiders is likely wearing power armor. In the room with the turret, there is a bookshelf with a mini nuke on it. In the corner is an elevator that heads back down into the entrance area.
In the building, there is also a hidden room with a skeleton surrounded by three teddy bears. To get to the hidden room one must have a jet pack (or use the tcl command in the console (pc) - walking on walls glitch will not work here). The hidden room is situated to the east, through a hole in the ceiling in the room leading onto the main area where the mirelurk queen spawns (on the middle floor). The hole one must enter is above the sloped floor where the ceiling has fallen in. Approaching the skeleton will trigger a chilling piano note.
- Raider atrium key - At the raider base, in a metal box in the enclosed area behind a turret. Opens shack type door.
- Several mirelurk eggs.
- Overdue book - Leaning against the side of a desk with a terminal on it, in a room with a partially collapsed ceiling and a mattress, west of the hall with 2 lion statues.
- Fusion core - On the bottom level, in the room with a terminal that opens a security door visible through a hole in the wall.
- Mini nuke - On a bookshelf in the room right next to the elevator.
- Raider power armor - On a raider commander, in the final room before taking an elevator back to the surface.
- Vault-Tec lunchbox - In the room just before the raider commander and turret due east of the table with three chairs and a bunch of loose caps on top.
- Day Tripper - In the northwest corner of the room that the elevator lowers to - tucked behind the bookshelf.
- State House note - On a dead scavenger in a room with a terminal on the second floor.
- Road to Freedom: The Sole Survivor has heard of a group that aims to take on the Institute and only has the clue, "Follow the Freedom Trail." To find the Railroad, they have to start at Boston Common.
- Without a jet pack, once the player character jumps down the large hole in the atrium to the large pool at the bottom, the player character will be forced to advance their way through the mirelurk infested basement and upward through subsequent raider base in order to be able to exit the statehouse. Player characters wishing to exit ASAP will not be able to do so until they reach the catwalk that is across the upper side of the atrium and then drop/jump down to the lower edges of the hole. In Survival mode one should take note of the fact that there are no beds to sleep in from the pool area until the end of the raider base.
- The mirelurk queen will only spawn once the metal doors have been unlocked via the terminal near the fusion core generator and afterward, the player character either approaches the pool proximate to the terminal to the north or the player throws an explosive into the pool. Those who wish to avoid the mirelurk queen altogether can safely access the unlocked hallway by returning to the pool area via the mostly irradiated path leading up to the terminal.
The Massachusetts State House appears only in Fallout 4.