Fens Street sewer The Fens Street sewer is a location in the Commonwealth in 2287 , and is located fairly close to Diamond City . Background . Inside , a serial killer dubbed the Fens Phantom has built a menagerie of horrors to portray his kills to an unnamed detective on his trail . Following the holotapes left by the murderer , the Sole Survivor can learn about the killer ' s interest for the detective , leading to his ultimate demise . Layout . Exterior . Access to the sewers is gained via a manhole to the north of Diamond City . Take the exit to the west of the main gate and head north , turning west at the scaffold ramp into a side alley . The entrance is surrounded on 3 sides by railings , within their confines is the manhole cover , a toolbox and a skeleton . Interior . Upon entering , turn the right at the end of the short corridor , where one can see a skeleton trussed from the ceiling with an " x " etched on the wall . Next to this a side cabinet with a toy car , toy rocketship and the first dear detective holotape sat on the top . There is also 2 wooden block s and a toy truck on the lower shelves . Looking to the right while approaching the skeleton , a skull and arm can be seen protruding from the wall . Turning right from the cabinet and heading down the slope , the area opens up into the sewer itself . On the left a headless skeleton is sat on the wall arch , propped up by a toolbox , holding a fishing rod and a skull fixed to the hook . Below the pelvis " xx " has been etched onto the wall . Head down into the water and turn right , following the flow of the water , which contains three feral ghouls . Halfway along the sewer path here , one can see a skeleton on the floor between a toolbox and a radio . Just above them there is a single " x " on the wall . Exit the water from the ramp at the end and follow the path through the narrow pathway , veer to the left and a skull can be seen on a barbecue , next to the second dear detective holotape . Looking to the west of this display there is a cooler and a makeshift battery . Turn back to the east and head left upon reaching the far wall . Follow the pathway into another sewer section , making a right turn in order to head down the stairwell and into the water , which contains several barrels and two bloatflies . Take the steps up to the far left and head through the corridor on the left hand side . Shortly upon entering the corridor , the path forks in two directions . The left hand fork leads to a dead end , blocked by a grate . However there is a matress at the top and several items of food in a shopping cart . Heading straight on , then turning left leads out into the next section of the sewers . Upon entering this section , one will see a cymbal monkey and a skeleton with a brahmin skull wearing a bowler hat sat on the ledge , glancing to ones left there is five baby strollers . Head over the bridge and up the slope , turning right and following the wall into a new corridor . At the end of this corridor is a gas filled room with 2 mannequins and a skeleton on a pallet at the far end with a chair and side table before the . On the table is the next dear detective holotape and a 10mm pistol . Make a turn u - turn and continue through corridor , which will open up into the upper section of the room with the strollers . Head up the ramp and follow the pathway to the right . Partway up the wooden steps and dog kennel with a human skeleton can found inside . Continue past this and turn left at the top , where the final corridor can be seen at the far end . upon exiting the corridor , one is in a maintenance area containing several feral ghouls and a glowing one . There are several side rooms in here , the first room , which is due to south from where one enters the area , contains the final holotape , a copy of Tumblers Today and an Expert locked safe . To the far west of the main room is a red steamer trunk . heading up the stairs and following the winding linear path will lead back into the room with the skeleton fishing with a skull . Appearances . The Fens Street sewer only appears in " Fallout 4 " .