Sandbox

Sandbox is upcoming map that will be included in the Mythic Map Pack. It's name has lead many to think that it will be a similar map to Foundry and Sandtrap. The level's hidden skull logo, a Monitor, supports the theory that the map will be Forge based. The logo may also have been chosen because the map is Forerunner. In certain Bungie.net forum posts, there have been repeated queries as to whether there will be a larger version of Foundry, and in some cases, Bungie staff or higher ranked members have replied and said that there was one in the works.

Sandbox along with Assembly and Orbital have been confirmed to be shipped with the Limited Edition of Halo Wars. Bungie has confirmed they are working to get these maps available on Marketplace as soon as possible after Halo Wars' release on February 27, 2009. The release date for the other three maps is unknown although it is thought that they will come with Halo 3:ODST.

In a video shown by Bungie, one of their employees cuts it off at the end when a giant spacious room similar to a VR range is shown. This could mean that Sandbox might allow you to add in different backgrounds, floor styles and make your own map without any hindrances.

A brief clue to its place in the Halo universe was posted by Lukems on 01.20.2009 2:40 PM PST: "Forerunner structures are often so vast, so towering and so exaggerated that they'd be visible from a number of different excavation sites." This may mean the large tower could be the tower of Epitaph.

Skull
Sandbox features a hidden skull, Sandbox Skull. This skull, when claimed, unlocks the Sandbox Skull Achievement. The crest of the hidden skull on this level appears to be a likeness of the Monitor, furthering suspicions that this will be a Forge-heavy map.

Trivia

 * On Bungie's video designed for receiving the game of the year award on G-4's G-Phoria, the Bungie crew was seen standing in a strange new place. This zone was suspected to be Sandbox.
 * This map may be a larger outdoor version of Foundry.
 * According to Bungie, they stated that "...when Orbital and Sandbox peak behind the curtains, that day won't likely be a Friday." indicating that like the previous DLC maps which were revealed on a day that wasn't a Friday, it is possible to assume that Sandbox's first official appearance may be on a Tuesday somewhere in late January or early February 2009.
 * Sandbox still remains to be the only unrevealed map in the Mythic Map pack bundled with Halo Wars: Limited Edition. Assembly and Orbital have been revealed.
 * In Luke's sketch, if you look at the horizon just to the left of the large structure on the right, you can see a person holding what looks to be either a Beam Rifle, Sentinel Beam, or a Brute Shot.
 * Another theory about Sandbox from Luke's sketch is that aside from being a fully forge-able map, it could be just a large, somewhat flat map with many materials. Either that or just a large Big-Team styled map (very much like Sandtrap) in a night-time setting.