The Sewer

The Sewer is the third chapter of the first campaign, No Mercy.

In this chapter the survivors begin in a safe room with the usual tier 1 weapons. Upon leaving the safe room, they make their way to an old warehouse. In order to enter the warehouse, the survivors must activate a lift which is noisy and attracts the horde in a mini-finale, or it is possibble to bash in a cargo door(see Trivia) To the right of the lift is a gas station; the gas station explodes if shot at, killing anything underneath it and incapacitating nearby survivors. Special infected need to be directly underneath it to die, otherwise it merely knocks them back. After fighting through a storage room and reaching the generators, the survivors then go through a man-hole to reach the sewers. After fighting through the sewers, the survivors emerge across the street from the hospital. The survivors can then enter a safe room at the base of the hospital.

Trivia

 * The sewers is one of the most modified maps in the history of Left 4 Dead. Several older versions had players go from warehouse to warehouse, through a gas station market, and even up a truck to get into the main sewer enterance.
 * If you look closely when you get to the warehouse, you can see the helicopter land on the roof of the hospital, possibly hinting there were other survivors that were in the city and contacted the pilot. It may also explain the pilot's "incident" in the rooftop standoff.
 * There is a door underneath the roof the survivors go across to get into the sewers. The door can be opened with a button on the other side, a tank punching his way through, or repeated meleeing by the survivors. (not recommended during versus since it is an unfair tactic)
 * As a smoker in versus, it is possible to kill or incapacitate a survivor by pulling them off the roof(the one you reached on the lift). This either done by being on the ground or on top of the warehouse.