Taft Tunnel

This is an escape tunnel from Jefferson Memorial. The exit point is a sewer grate outside the Citadel entrance, just south of the west point of Arlington Memorial Bridge. These tunnels were most likely used as a secret escape route for Pre-war political figures occupying the Pentagon, but Chinese weaponry and items, including rifles, pistols and clothing, alongside a HAM radio and other bits of technology, lend credence to it being occupied by Chinese spies.

Notable loot

 * Chinese Army: Special Ops Training Manual on the desk in the room when you first engage the Enclave Soldiers. There is also Sugar Bombs, a Chinese Assault Rifle, a Dirty Chinese Jumpsuit and a Chinese Commando Hat next to the book.
 * Nuka-Cola Quantum in the second section of Taft Tunnel. Found after Dr. Li stops you for Garza, next to a portable generator sitting on top of a wooden picnic table.
 * Nikola Tesla and You behind the generator immediately next to the Nuka Cola Quantum.
 * Eyebot Helmet in the second room you are ambushed by Enclave Soldiers
 * A pair of Reading Glasses can be found next to the makeshift bedding in the room directly after you see the first non hostile Eyebot.

Inhabitants

 * The lower levels have a fair share of Feral Ghouls.
 * The floors above have many Enclave Soldiers.

Inaccessible location access
The upper and apparently unreachable floors with Enclave soldiers can be reached with careful barrel stacking and several strategic jumps. The exit point has a ladder and a sewer grate that doesn't work (you can open the ladder, then close it again if it pleases you).

This catwalk allows passage between the two high-vantage ambush points via a door to "Taft Tunnels" up in the "unreachable" level. If you haven't been to the second yet, this lets you ambush the ambushers! See the image sequence below for the exact method.

Xbox360 and PS3 players can access the inaccessible area by kicking a barrel (which can be found in the surrounding area) in to the corner of the room (below the catwalk leading to the upper level of the inaccessible level) use the barrel to jump on to the pump housing (this may take a little bit of time)walk into the corner and look up towards the bottom edge of the door and look around the area slowly until the 'open door' prompt appears

Bugs

 * Sometimes when re-entering and exiting the Taft Tunnels after the the Waters of Life quest, Dr. Li and her team of scientists may appear outside of the Citadel and next to the tunnel entrance.
 * On the Xbox360 when going through the door in the inaccessible area, Dr. Li, Daniel Agincourt and Alex Dargon may all appear in the second area of Taft Tunnels and act as if they were in the Citadel.
 * on Xbox360 (and possible PS3) try not to re-load save files as the two Enclave soldiers on the catwalk to the inaccessible area may dissapear and all your hard work will be fruitless.
 * On the PS3 & 360, when you approach the sewer grate for the first time you may be attacked by a super mutant. If you kill the super mutant with an energy weapon and it becomes an ash pile on top of the sewer grate, you will not be able to enter the Taft Tunnels. Your game will be corrupted and will have to reload from an earlier save point.
 * On PC, if you successfully convince Dr. Li to abandon Garza and proceed to the next section, the remaining members of the science team can turn into Sergeant RL3 (who was waiting in my Megaton House) and the mission proceeds normally.
 * It seems if you pull a sneak attack on an enemy, someone from the team thinks your being reckless, sometimes they will run away from you temporarily, and Dr. Li will crouch regardless of what stance you are in. This changes nothing but can be fixed by asking her to follow you again.
 * If you scout ahead and leave Dr. Li and the others, often, your followers (if left somewhere and told to wait) will appear in the tunnels at the second entrance point. They will continue to wait there (except Dogmeat, who returns to Vault 101), unless you find them and lead them out. (PS3).
 * After completing the game and entering Broken Steel, if you attempt to backtrack through Taft Tunnels to the Jefferson Memorial using the barrel and catwalk trick, you can see through the fenced in area next to the "useless" ladder that the Enclave's force field is still active and blocking the door. (Xbox360)
 * If Dogmeat was told to wait somewhere (in my case super duper mart) he may appear if you tell Dr Li to wait, then travel way ahead, (Into another section) and then go back to Dr Li. he is waiting next to her.