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"You're lucky you've got that hazard suit, this water's nasty. Got room for two in there?"
Alyx Vance[src]

The City 17 Underground is a series of dark underground tunnels, parking lots and storage areas introduced in Episode One.


Ep1 c1700 tunnel

Dilapidated tunnel with Ceiling Turrets with empty magazines.

Following the Combine invasion and the Seven Hour War, the City 17 underground was apparently no longer used and fell into serious disrepair. However, it is possible that Resistance members used the underground even before the rebellion, as there are numerous bodies to be found, only some of them being recently deceased.

After the destabilization of the Citadel, the underground becomes severely infested with Headcrabs and Zombies, as well as Antlions, who, following the collapse of the Combine's defensive field (previously powered by the Citadel), start establishing a foothold in the city via the tunnels.

Because of the large number of Zombines in the underground, it is possible that the Combine were attacking Resistance members hiding there when Antlions and Xen wildlife were allowed access.


The City 17 Underground mostly consists of underground parking lots, maintenance tunnels, and storage areas. All or most of these facilities are in serious disrepair and many are infested with Zombies and Xen wildlife. There are many storage rooms and lots, as well as sewage pipes. The passageways connecting other areas also contain handwheels to open gates.


Zombine dark

A Zombine running at Alyx and Gordon with a grenade.

Half-Life 2: Episode One

After stabilizing the Citadel long enough to make their escape, Gordon Freeman and Alyx Vance become trapped in the underground after the Razor Train they are riding in derails and crashes. After battling hordes of Zombies, swarms of Antlions, and overcoming various other obstacles, Gordon and Alyx are able to locate an elevator, which they manage to power up and ride to the surface, escaping the hordes of Zombies. Almost arrived to the surface, they have to find a handwheel to unlock the final gate, after which they discover how much more City 17 is ravaged and that Isaac Kleiner took over the Breencast network to deliver vital information to the city's inhabitants.

Behind the scenes

Alyx helpless

Alyx helpless without Gordon's flashlight.

  • This chapter is the first example of Alyx's new co-op features and combat abilities.[1] As she is the only protagonist equipped with a gun, Gordon having only the Gravity Gun (although he originally was to have no weapon at all[1]), he has to help her killing enemies by aiming his flashlight at them in dark areas, otherwise she does not see them and thus cannot defend herself properly and could get herself killed. He can also throw objects at enemies, but Alyx will always be able to manage all the attacks on her own with a minimum of support from Gordon. She also cannot move in the dark if Gordon disappears with his flashlight turned off, and will call for him helplessly, in a scared tone.
  • Gordon originally couldn't operate the power boxes in Episode One and would have to wait for Alyx to do it. But developers removed this due to the fact that this exposed Alyx's most robotic tendencies. Gordon would've had to let Alyx finish what she was doing first and then wait for her to work. This led to frustration. What developers learned is that in order for Alyx to be more reliable, she has to finish a task quickly and then move on.  
  • This chapter also first introduces the Zombine.
  • In completely dark sections, Zombies will tend to spawn faster if the flashlight is turned off.
  • In completely dark areas where the flashlight is the only source of illumination, the team found that they would often end up with grossly over-exposed views and the HDR parameters were to be modified. In particular, they drastically shrunk the region of the screen where the flashlight's light is located, which is bigger in Half-Life and Episode Two. It permitted them to concentrate only on that area and thus increase the sense of claustrophobia.[1]
  • In that chapter, the player is also forced to block Antlion burrows with cars in a collapsed parking lot, while Alyx helps him fight the Antlion, but without giving him any clues on how to block the burrows.[1]
  • The elevator scene is one of the most tricky parts of the game for the inexperienced player. When Gordon and Alyx arrive at it, its power is down and has to be reactivated through a powerbox located at the other end of a big and completely dark room. When the power is turned on again, Zombies swarm the area, and Alyx and Gordon must bear a huge standoff while waiting for the elevator to come, mirroring scenes from previous games such as the teleport scenes at the end of Blue Shift or in the Half-Life 2 chapter Entanglement. The first iteration of this battle was originally very different. The space was larger, had water in it, and was not completely dark. The team cut water in favor of more Zombies, as Water is relatively expensive, performance-wise. The area was made smaller to ensure that the player would see the elevator and recognize the problem that needed to be solved before the fight starts. The team applied a completely dark setting in order to enhance tension and to leave the battle as a final test of the players' low-light fighting skills, which had previously been developed over the course of the episode. Finally, they added a wire running along the ceiling from the elevator to the powerbox to give the player a guide as they familiarize themselves with the area.[1]
  • The City 17 vista where Kleiner is seen on the Breencast after reaching the surface is intended to be "an explicit visual reward for surviving the elevator battle."[1]


  • Although Freeman goes through an underground area after Alyx is kidnapped in Half-Life 2, this area is not considered as the same City 17 Underground, the latter consisting more of sewer systems and factory floors.
  • Even if the player is fast enough to turn the powerbox on before Alyx presses the elevator button, the light of the elevator will still turn off.
  • Despite the area being infested with Zombies, the Poison Zombie is the only zombie class that did not appear in the elevator scene due to balancing reasons. The Poison Headcrab however, does appear in the stand-off, but only in a small number.
  • Because of the darkness in the underground. Alyx will rely on Gordon's flashlight in order to proceed and attack enemies. However, to balance this, Alyx has a higher health than usual, so it is harder for her to die. Also, unlike in Half-Life 2 where she will always chase and kill enemies and then follow the player, here, Alyx will not chase enemies unless they are close to her.
  • Alyx may sometimes joke by making a zombie sound. This can be easily noticed when the game is fully captioned. If the player turns around to check, Alyx will say "Gotcha".


List of appearances


Preceded by
Citadel Core
Half-Life 2 story arc journey Succeeded by
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