The Fens street sewer is an indoor location. 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.
The sewer has a winding yet straightforward path, reminiscent of a haunted house ride/tour. Simply follow the path to the end and admire the props along the way.
- Four audiologs, the Dear detective tapes, can be found along the path with many dead bodies in peculiar postures. Each has a white 'X' chalk mark on the wall indicating the body count.
- A flamer - In a hidden alcove behind the glowing feral ghoul, behind a chain fence.
- Tumblers Today issue #2 - At the end of the zone near a safe and the last tape in the "cell" area.
- A Stealth Boy - Right next to the Tumblers Today magazine.
- An X-cell - In the first room near the fishing skeleton, across the water in a blue basket tucked behind a gray pipe and a blue pipe.
- A Vault-Tec lunchbox is at the opposite end of the tunnel from the skeleton with the fishing rod. It is in the water just past the metal ramp in a cluster of three blue crates. It may be underwater. A second one is in one of several baby strollers near the "XXXX" on the wall.
- A dog collar located around the neck of a skeleton inside a dog house towards the end of the sewer.
- In the room with radioactive barrels in the water, jump onto the horizontal blue pipe on top of the stairs to gain access to a weapon stash near an activated radio to the left. The radio is turned on and can be heard.
- If Strong is brought here, he will speak of a time he and his brother ate a human in the sewers.
- In the last room with the skill magazine, the Sole Survivor can jump off the pathway to a small alcove with a mattress, machete and a skeleton couple. This mattress cannot be slept on. Assuming the story told in the holotapes is true (especially the fourth part), this may show the dramatic result of the detective's investigation.
The Fens street sewer only appears in Fallout 4.