Rat's Nest is a large indoor vehicles map that resembles an area from the campaign level Crow's Nest, with internal vehicle accessible roads, tight corridors, walkways suspended above areas and vents. In the distance, Pelicans and Hornets pass by. "Rat's Nest" is the colloquial name for the ammunition storage facility of Crow's Nest and was used by the UNSC to store munitions and fuel up until the Covenant attack on the base.
On November 19, 2007, Microsoft released information regarding the first Halo 3 Heroic Map Pack. Rat's Nest is one of the maps included in this bundle. The map pack retailed for 800 Microsoft Points (US$10), and was released on December 11, 2007. However, on March 25, 2008 the Heroic Map Pack became free to all Xbox Live Members.
This map is, essentially, a big figure 8 track (note, a digital 8, meaning vehicles must turn 90 degrees to cross straight from one side to the next). The map is extremely open and vehicle-based around its perimeter and center, with close combat and medium-sized rooms everywhere else. It has two Warthogs and Mongooses parked outside of both bases. Small rooms connect each base. Around the edge of the map there is a small outdoor road.
On the upper road there is a Ghost and a sniper rifle. Below the upper road, there is an active camo. A gravity hammer and a machine gun turret are placed above that, providing a commanding but exposed view. The rocket launcher is by the cliff. A Pelican is positioned on a landing platform visible from the track, but it is unusable and inaccessible due to death barriers.