Nebula

Nebula is a Halo 2 Anniversary multiplayer map intended for use as a Forge canvas. It is one of three skybox-only maps created for Forging; the playable area consists solely of an expanse of open space, surrounded by an asteroid belt. The map's skybox is identical to Halo 4's Impact Forge map.

Trivia

 * Along with sharing the skybox with Impact, the descriptions of the two maps may also imply they are the same location.