The Underground

"It's a hole! Oh, excuse me, a historic hole."

- Nick

Underground is the second chapter in Left 4 Dead 2 ' s The Passing campaign. The Survivors exit the safe room and head through streets and a bar that contains a jukebox until they reach the historic "under the river tour". The second phase takes you through a sewer that has two gates that when opened activate a alarm. The survivors must run to the safe room while being slowed down by water and hordes of infected.

Campaign
In the beginning of this chapter there is a high chance that a Fallen Survivor will spawn. Take to time to carefully turn off your flashlight and snipe it, this will give you some supplies right from the start. A lot of foot lockers and one M60 will always spawn. There is also something that may surprise you on your way: when you reach a fence covering a road you will hear an oncoming truck. When you put the game in slow motion you will see the Midnight Riders' tour bus.

There are at least three separate points of no return within the last leg of the level: One being the stairs leading down into the sewers and the other two being both of the starts in the marathon gauntlet. Use extreme caution when dropping down from each of these points.

There are several parts in this chapter that the Infected can really do some damage and most likely cause your team to die, especially Tanks, Smokers, and Jockeys.
 * The first one is the stairs right outside the safe room. A Fallen Survivor will almost always spawn here so try to take him out before venturing further, because especially in Versus, there might be a Boomer or Spitter camping in one the alleys next to the stairs, so try to have a Survivor on point to check it out. If they get puked on, have them head back up to the safe room, and have the other non bile covered players cover them.
 * Next up is the Construction Site. Most likely there will be either a Horde, a Witch, or other Special Infected that could easily pin down a Survivor, and if the team isn't fast enough they could get incapacitated or dead, because the others might be already in the Pool Hall. The area is also a Swamp-like terrain, which will slow all Survivors down who don't have Adrenaline.
 * Speaking of the Pool Hall, there will be a jukebox which will get you an achievement but also cause a panic event. In that case, if you have been playing through the whole campaign, there should be tier two guns and possibly a foot locker, so camp in a corner and wait it out. There very well may be a Tank, so a very good tactic is have the healthiest player attack the Tank first, and lead to one of the pool tables, and have it chase you around the pool table while the others open fire and light it with molotovs or cover them with bile bombs.
 * Next one is the plank outside of the apartments that leads you to the streets. This an obvious spot for Smokers and Jockeys to take out one of your team, and an exploding Boomer could take out a whole team. Just don't drift far ahead, act quick if someone else is pinned, and you'll be fine.
 * After that, the streets will sometimes spawn a Tank. It's an open area, so it shouldn't be to difficult. There might be gas cans in the Jazz Club so have one person get those and light it up.
 * The Under the River Tour is a Jockey's paradise. There are many dark rooms that the Jockey can lead a Survivor to very quickly, so try to have all four players be almost right next to each other so a Jockey can't surprise attack a stray Survivor from behind.
 * After you drop down the stairs, if a Tank hasn't spawned yet, it will here. Just try to confuse the tank by firing from all directions and moving around. If you try to go a certain way, it will most likely catch up to you, being it's a Swamp terrain as well. If the tank comes near, dodge his rocks or just hold out until it dies, because the others should be focusing fire on him.
 * The gauntlet should be a breeze, have someone with an Auto Shotgun or M60 go first, to clear out a path way. If this doesn't happen, the Common Infected will endlessly swarm until you make it to the safe room, so have one person stray forward while the others are behind him distracting, as a secondary option.

The Survivors
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The Infected
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Survival
There is a glitch in Survival whereas the player can reach an invisible ladder leading to a balcony.

However, the Infected cannot reach the Survivors, and the only danger are Smokers and Spitters, but these can be avoided by staying off of the railings and crouching in the center of the balcony.

To get to this balcony, the player must travel towards the underground tunnel area. This will be blocked-off in Survival. There should be a neon-light sign hanging above the closed-off entrance to the tunnel; next to this sign is the Jesus-room balcony. The player should travel to the right of this balcony, next to the ivy. The player party should approach the ivy from the parallel brick wall. This will take a few attempts, but the players should discover an invisible ladder that leads to the balcony.

Once you figure out the ladder and become comfortable with climbing it, send someone to start the radio. The rest of the team should cover them as they return.

As long as the player party takes out any Smokers or Spitters, they will be untouchable on this balcony.

If you choose to play this without a glitch, a tactic is to stay at the spawn area and close the doors. Have two people guard the entrance to the streets, two people guard the entrance to the construction site. If you do this, by the time the tank arrives you should be at full or almost full health. then have someone head to the streets with a gas can and every one else follow. If it doesn't spawn on the streets, have two guard the entrance it will come in and place the gas can there. Shoot the gas can, light the tank up, and you shouldn't have taken damage. If you follow this you should get a bronze medal at least. It's recommended to have at least two people doing this.