Foundry

Foundry is a multiplayer map released for Halo 3 as part of the downloadable Heroic Map Pack. It was made available on December 11th, 2007. It was made exclusively for Forge, as almost all features of the map can be changed, deleted, or even replaced by any object that Forge has allowed.

Description
There is no set description for Foundry, as it can be Forged into almost any configuration imaginable. The default configuration of Foundry is a mostly close-quarters, two level map with a few long hallways. The power weapons are distributed into the corners and center of the map. The Rocket Launcher is in the center on the second level, there are Brute Shots in each base, and Sniper Rifles are in the corners opposite the bases.

There is a crane on this map, as well as two shipping areas: A and B. Most of the boxes have "P425" printed on them, indicating possibly that that section of Foundry is Section P425, or it could be a serial number of some sort.

Getting out of Foundry
To get out of Foundry you first must be in Forge. This is much easier if everything is deleted beforehand. Become a monitor and fly into one of the windows, while holding forward and slightly up you will slowly move up the window. You will stop underneath a small ledge; continue holding the control stick and create a respawn point. If you followed the instructions correctly, you will see your respawn point outside through the window. You can then commit suicide and respawn out of the map. Once outside of the map you can create teleporters and move around outside of the map.

Be warned, many places you step outside of the map will cause you to either be killed by the Guardians or fall to your death.

Foundry Recreations
Foundry has become the best map to recreate maps from Halo:CE and Halo 2. An easy way to search them is Halo 3 File Search

Trivia

 * In the trash found on the floor, there is a blue draft notice paper and a pack of cigarettes. In a different pile of trash, there is a purple hippo that is hard to see without aid from the sniper rifle.
 * On top of the crane, there seems to be a Forerunner glyph. It is clearly in the shape of a body, but it is neither human nor Covenant.
 * If you get past the fence behind the blue room, there is a poster of a soccer ball saying "It Glows".
 * FACTORY CPLX 09 is located on the edge of a lake, opposite the lake there is another factory. If you escape from the "foundry" building and zoom-in on the factory, you should see the words, "FACTORY CPLX 71" on the side.
 * P425: the serial number on the crates. 4+5=9. 9-2=7. 5+2=7
 * Foundry is rumored to be the assembly line seen in Arms Race.
 * Supposedly, a dead brute body can be seen behind the map.
 * On the wall without windows you can see the name Voi. Most likely this means that Foundry is geographically close to The Storm mission in the campaign.
 * There have been many sightings of the Ghosts of Halo on this map.