Franklin Metro Utility

 is a few Metro utility tunnels, part of the Metro track tunnels, and a cave system. It's slightly irradiated, heavily so in some places, and partially waterfilled. The Metro track tunnels are a section of the Blue Line east of Franklin Station.

The tunnel loops back onto itself, and you can drop down a hole in the floor to reach the beginning after you've been through. Be warned that it's quite easy to become stuck in the dumpster that the player drops into.

This is an amazing area to loot if you're into creating items at workbenches. Not only is there a workbench in the first room and at the end of the loop (before you drop down) but there is one of almost every item you'll need for your creations.

Inhabitants

 * A lot of Feral Ghouls and Glowing Ones.
 * For those with Broken Steel installed, be very careful entering this area if your character's level is higher than 20. At the extreme end, every single ghoul, bar one or two Roamers, will either be Glowing Ones or Feral Ghoul Reavers, and due to their proximity you may be attacked by a group as large as five at once, particularly in the heavily irradiated tunnel. It is advisable to bring a powerful follower, such as Fawkes or Star Paladin Cross, or wear the Ghoul Mask to render them friendly. On the other hand, they are worth a lot of XP if you kill them all.

Notable loot

 * Five Stealth Boys (including the one mentioned at map point A, see below).
 * Two are directly to your left when you enter the area, in the doorless metal tool closets.
 * One is at map point A
 * Two are at the top of the map (where it loops around) on a shelf before you drop back down to the beginning.
 * Two Pre-War Books in the upstairs part of the first room, in a bit and slightly to the left of the entry/exit door and immediately to the right of the open dumpster with the empty oil drum (if you look above you, this is also where you will eventually drop through at the end of the tunnel loop).
 * Tumblers Today near the door to Falls Church/Mason Dst Metro. It's in the downstairs part of the first room to the right of the turret. The book is on top of an average locked mine box where you fight a lot of glowing ones.
 * (A) Guns and Bullets, downstairs in the center of the second room (not the one with the turret) on a desk, along with a Stealthboy.
 * (B) A very handy Advanced Radiation Suit and a Mini Nuke can be found underwater, at the end of the waterfilled tunnel.
 * (C) Burnmaster in a heavily irradiated end of the tunnel, in a trailer (there is also a Nuka-Cola Quantum next to the Burnmaster) They are both guarded by two Glowing Ones or Feral Ghoul Reavers.
 * (D) U.S. Army: 30 Handy Flamethrower Recipes in a bookshelf.

Bugs

 * A ladder in the south tunnel appears to lead to the surface. You can open and close it, but doing so has no effect.
 * At some point in the game your X-Box may freeze while trying to enter, if you reload a previous save some time ago, you will still be able to go in, but not in your latest save.