The initial hallways of the map are all meant to be unused or deactivated maintenance and storage rooms, and upon reaching that first road section inside a huge cave, you can see two of the tunnels barricaded as well a wreckage of military vehicles in the other. The reason for the barricades is due the military going to seal off the place from the common infected since those roads are tunnels that leads to alternate surface entrances, entrances that could be overrun by the infected and indeed were.

After going some levels up by using the stairs and ladders in those maintenance hallways, the survivors pass by a corridor with a .50 Cal and a huge trail of bodies, Zoey asks the others if they think anyone is still alive because the loner survivors they heard during their time waiting in the initial room, and that corridor brought her into doubt that they are last ones.

Right after that corridor, upstairs there's a peculiar room which some people will get the reference right ahead, or maybe when turning to the left and going behind that forklift with a radio playing a song, that particular song is called "At Doom's Gate", and yeah, it is a music from the very first Doom game, that entire room with the ladder and the other with the four columns are literally the first rooms in the first map in Doom, that's also why Francis says "Nice place" when going nearby the radio location.

Going upstairs the survivors are met with an armored door that opens by pressing and holding, this is a minor detail but that warning right above the button is made by me and it tells that door will forcibly close if the main gate is in motion, which is the first mega event the survivors have to deal with. That Reinforced Gate itself is one of the access points to the Research Division of the facility, so the survivors were in the Military side and hopped into the Research one by crossing that gate.

The wreckages of military vehicles found in the tunnels in that road cave and after the reinforced gate were due the despair of people trying to survive and drive these vehicles while the infected were attempting to invade.

Trivia:

• I think only close friends to me ever knew this before, but this map was my very first one, which introduced me into Hammer and proper Left 4 Dead modding.
  
• The cave road with the buildings and tunnels in it was an addition made in the last iterations of the map before the initial release of the campaign, previously opening that door which leads to the road would directly lead to that maintenance corridor when going upstairs in the cave.
  
• The loud horn sound the Reinforced Gate does is entirely crafted by me.
  
• The track that plays during the Reinforced Gate event is a track i extracted from Hellgate Global (the MMO version of Hellgate London that had an expansion which is set in Tokyo), that track alongside all other tracks that plays in the Tokyo parts of the game are not composed by the original composers of London (which are Cris Velasco and Sonic Mayhem), so currently not even myself knows the name of this song and neither the original composer.

Going a couple storage rooms and hallways, the survivors are met with a very huge room that looks like a dam, that sector is where the water supply of the entire Research division comes from, anyway, all the elevators they pass by are either not powered or broken, this leads them to go back a couple floors down again, going into the room with a generator, and yes, that is a The Walking Dead reference with the "Don't Dead Open Inside" properly fixed.

The generator room is supposed to be a dead end, in exception of the Old Tunnels access, which of course is the only path at this point. So for everyone who wonders what are these shadow people, all this mysterious aura the Old Tunnels emits and all the spooky sounds that can be heard on it, many is going to hate what i'm about to say, but there's nothing really supernatural in that place, the tunnels just have a leaking hallucinogenic gas that instigates fear (yeah similar to Scarecrow's fear gas), this is why the infected are there and not giving a ♥♥♥♥ to whatever the survivors are witnessing, the gas doesn't affect them.

When reaching the end of the Old Tunnels section the survivors are met with an elevator that yes, plays "that siren", which is the Silent Hill siren from the movie, but edited to have an echo effect to feel like its coming from the tunnels.

Trivia:

• This level was going to be more of what the previous one was, but i decided to break up the pacing little by making the Old Tunnels section, with it being more horror than action driven.
  
• The posters found in some of the rooms along the Old Tunnels are movies which inspired me to make that section the way it is.

Walking a couple rooms and corridors the survivors enters a big hall with lots of dead bodies. Obviously this is a teaser of what is about to happen, however when going into the small security office in the left, the survivors can interact with a walkie-talkie, that actually plays audio recordings of the soldiers who fought the infected in that big hall. Since they didn't know how to deal with the special infected at this point, they got overrun quickly during that battle. In a last attempt to save the facility from being invaded even more by the infected coming inside, the remaining soldiers closed the shaft doors and shutdown the energy of the main hall and elevator.

The survivors job in this chapter is to restore the energy, open the elevator shaft doors and call it, so they can leave the facility once for all. What they didn't know is that the facility have the lockdown systems active, which calling the elevator makes it plays the perimeter alert horn, this basically attracts almost every infected inside the research division towards them, thus starting the mega event.

After the intense fight to finally leave the place, on the upper end of the elevator shaft there's another road system, which again is explained that the military were sealing off one of the sides to prevent the infected breaking through, while the other side is full of wrecked cars and buses, that is due the civilians despair to enter the bunker when the invasion wave started. This leaves only the maintenance path that leads to the Train lines and one of the secret entrances the facility have. Many players directly goes in the maintenance path and don't even fully explore that road, this ironically showed me how many players are actual map explorers, that place have plenty of resources in the security outpost and between the excavators in the blocked left road.

Trivia:

• The elevator event is heavily inspired by The Sacrifice comic, more specifically the page 123's main panel, but instead of climbing up, the infected comes down.
  
• This level have couple rooms inspired by some module rooms found in DOOM(2016) SnapMap
  
• Just like the horn sound of the Reinforced Gate in the first chapter, the horn sound of the Elevator is also entirely made by me.

After that elevator linking the secret bunker passage with the basement of a Steel Industry, located in a long and desolated road. The place is entirely open, and the tunnel in the left when going out the Steel Industry have a bus parked that blocks the passage completely, i have to say that this time that bus being randomly there was one of those lazy methods to tell the players that is not the way to go, however the tunnel by itself should link back to the bunker at some point going down. The entirety of the road section are completely guided by the lights, wherever you see light, there's probably resources there.

Following up the road, there's another dead end, this other tunnel have collapsed rocks that fell from the mountain above. Going to the left between the trees there's the barricaded entrance which leads to another bunker-like building initially, but things become sci-fi pretty quick in there with the blueish lights and specific architecture. That place is called The Maze, and by there the survivors keeps hearing loud background noises of things moving, that is because The Maze indeed move its geometry around as stated by the orange warning paper glued in the wall before entering it, but barely any player read that thing i guess. These sounds can be heard so often because the infected that invaded the place are currently triggering every sensor The Maze have, making it change shape again and again, producing more loud noises and attracting more infected from outside.

Going deeper into The Maze there lies a huge area that looks like a boss fight, build up mood for a boss fight and even plays a boss fight-like music once triggered. I guess i got the feeling right in this part, but no boss fight unfortunately. The scanner that scans the survivors are automated and currently only checks if the scanned object in question is a human.

Trivia:

• This was my first level at attempting to make external areas, i was still unconfident about how i would make it look the way it looks now, but managed to do it regardless.
  
• The Car Alarm in the road is just there as more sort of a joke because the whole space around to avoid it, and yet some players still have the incompetence to trigger it. And triggering it brings up a really huge horde as punishment for doing that.
  
• That entire place where you start the 4 Gates Event with that huge number 5 by the left wall is literally inspired by Section 7 of The Maze in "The Maze Runner" movie and that WCKD you can see after the gates in the truck parking lot is the same organization who built The Maze in the movie and are the current main antagonist of the thing.

The survivors goes inside the storage sectors of The Maze, and there's that weird beeping all over the place, that beeping is the evacuation alarm, all personnel of the WCKD have left the building, leaving only the infected that invaded due the loud noises The Maze does externally as heard in the previous chapter. When going right and passing by a deactivated metal detector, it is possible to see the full name of the organization that runs the place written in the wall, the "World in Catastrophe: Killzone Experiment Department".

With the entire place evacuated and not being secure anymore, the survivors goes through it and pass by an ammo pile with a graffitti and dead body nearby, again i guess every player just pass by it and don't really pay attention to the thing, but the truck you use the escape in the finale currently belongs to that dead guy and he left that message there before suiciding, the short backstory of him is that he went by the WCKD thinking they were handling the infected and seeking shelter there, but found no one, then The Maze started activating its geometry attracting the infected and preventing him from leaving in time.

After leaving the WCKD, the survivors goes through the woods and find an old building which teases to be the finale area with the four medikits and ammo pile, there's a small jumping gap to some stairs leading to a dark small room where you can find a family poster with a slogan "Quake is for everyone". Actually that entire small bunker is the starting room of the first map of Quake 1, hence why the image is in that corner as an easter egg.

The truck being the escape vehicle was a decision i took when i was still developing the second chapter, i have seen every possible vehicle inside the game's assets being used as escape vehicle. All the Helicopters, Crash Course truck, Death Toll police car, Jimmy Gibs car, the Boats, and even the static decoration vehicles in exception of that specific red truck. So i said myself "this one gonna be it". But turns out most of you actually found it anti-climatic and super "mediocre" for what the campaign have previously shown, especially after the event The Maze gave, the idea behind the entire scavenge thing and the truck was only the "reality is often disappointing" trope, something better was expected to happen as the finale, as some mentioned in the comments they were expecting:
1. Military rescue
R: The survivors just left the largest bunker in the entire east side of the United States, why are you expecting more military?

2. Gauntlet like the parish bridge but with some explosions sequences
R: Context where it is given, the military were overrun, only they could give such finale but all of them are dead by that time.

3. Regular finale but in an epic way like the events of Chapter 1 and 3
R: Did you ever imagine Tanks among that huge horde to kill? Because them alone would be rather easy inversely speaking as well due the firepower provided by the turret weapons.

4. Something like the 4 Gates Event in Chapter 4
R: Currently, i've been considering in add another finale, so this way i could bring the finale everyone is really expecting to be the "over the top epic" while the current one remains optional.

Trivia:

• During development i was seriously thinking if i should have included at least one forced panic event during the journey from saferoom to finale due the level being the same lenght as the others.
  
• Just like the Car Alarm in Chapter 4, the one lying at the entrance of The Maze is there just for fun. But less punishing this time due to being the last chapter.
  
• That cabin in the opposite side of the road where the Truck Garage is, is actually the Cabin from "The Cabin in The Woods" movie, i was going to make a generic cabin there but decided to make that specific one due the movie referencing Left 4 Dead, so i decided to reference it back in the campaign, at least by making the front porch and the living room similar to what is seen in the movie.

1. The initial idea i had for this campaign, was to make Millhaven Base itself. It would start from the prison cells in the underground levels, and end in the Train. However i decided not to, mostly due the vastness of the maps and Millhaven not really being this big. Making custom NPCs would also be a problem, due the extra characters presented in The Sacrifice comic.
   
   
2. While inside the facility, it may feel like Black Mesa Research Facility from Half Life. That is indeed one of the feelings i wanted to pass throughout the journey inside the complex, this military facility is intented to be big as Black Mesa in such case.
   
   
3. When going outside by Chapter 4, the night seems to be way darker than normal. The intention is to bring that original idea the developers had of having no fog to make the maps really dark, and much heavier in atmosphere due to that.
   
   
4. After the road section in Chapter 4, the original idea was the survivors burn the barricade that would lead to a small cave, then leaving that cave would purely go through a dense forest until they would reach a small cabin as saferoom for Chapter 5. I could see this entire part being super generic and dull to go through, so i decided to add The Maze from The Maze Runner movie instead.