Cold Stream

Cold Stream is the third DLC for Left 4 Dead 2. It was announced in a blog post on February 16, 2011. Cold Stream was released on March 22, 2011 in beta form on Steam, and it was officially released in its final form on Steam on July 24th, 2012. Cold Stream was released on the Xbox Marketplace August 3rd, 2012 for 560MSP.

Cold Stream is unique in that every chapter ends with a gauntlet crescendo event leading to the safe room. The finale, Cut-throat Creek, is also a hectic gauntlet event going through the entire chapter, like The Bridge from The Parish. Cold Stream is also noted for relatively few calm spots compared to other Left 4 Dead 2 campaigns.

Below is a complete list of video walkthroughs of the final versions of the 4 levels, with the first two levels in one video:
 * 1) Alpine Creek and South Pine Stream
 * 2) Memorial Bridge
 * 3) Cut-throat Creek Finale

Only for Left 4 Dead 2

 * Cold Stream, a community-made campaign from the creator of the 2 Evil Eyes community campaign.
 * Ports of Death Toll, Dead Air, Blood Harvest, and Crash Course.
 * Play all Mutations anytime you want.

Setting
Cold Stream takes place in forested area located deep in the mountains. Survivors make their way from the creek, passing the forest, and jumping into utility bunker fulled with infected for shelter. After resting for a while, they walk out into the stream and traversing a long stretch of never ending traffic jam of abandoned vehicles, before running down into a tunnel filled with restless infected and reaching another maintenance room for safety. From here, they must ascend from the darkness to the ruined bridge and make their way to the junkyard, while military bombs the highway above. Reaching the storage room, they call for extraction, and fight for their own life against a stream of a never ending infected horde and finally reaching a waterworks technical depot converted into a CEDA processing and extraction point. In a dramatic escape, survivors must climb upstairs (and fight a tank that occasionally spawns here) and finally escaping the place which is now surrounded by a untamed forest fire.

Graffiti
Unlike other campaigns in Left 4 Dead series, scattered graffiti that normally serves as a story telling mechanic appear very scarce in this map. Not only scarce, graffiti in Cold Stream also unusually appear disjointed and incongruent each other, so the story about the event what happened in the area can not be easily deducted. That is possible because of the places visited by survivors during their journey in this campaigns are places that normally restricted or unusually accessed by public (such as utility room, maintenance room, etc.) prior the Green Flu, hence not so much people knowing about it and passing through the places. With no much people passing, not much information left for the future passing survivors. These matched with the desolated and isolation vibes of this campaign.

Achievements
The Xbox 360 version of the Cold Stream DLC has no unique achievements added to the game.

Beta
Cold Stream was released to the public on the official servers on PC/Mac via beta release on March 22, 2011 for play testing and bug-seeking, such as finding nav-mesh bugs, navigational issues, hit box problems, missing zombie ladders, art problems, and more.

An in-game bug reporter was activated at the same time allowing players to send feedback and bug reports. This feature was announced by Valve to be extended eventually to work with other community campaigns. But strangely, there's no "Report Bug" button in the main menu or the in-game menu, which requires writing "bug" in the Developer Console yourself.

Players can also post feedback on the official forums in the Cold Stream section. Development of Cold Stream can also be followed on Valve's official Twitter account located here.