Intergalactic space
From Halopedia, the Halo wiki
Intergalactic space is the region of space between galaxies.
Installation 00 was located in the intergalactic void.[1] The Forerunners rarely ventured into intergalactic space, as they were satisfied with the resources of the Milky Way Galaxy.[2] The objects closest to the Milky Way Galaxy are the Magellanic Clouds, two small satellite galaxies where the Flood were said to have first arrived to the Galaxy.[3]
