Interstitial space

Interstitial space is known by many names across many cultures: "the Bad Place" by the hedolians, "the Scarlet Abyss" by Jezabelstein, and colloquially as "the Sandwich" and "the Pancake Stack". It is a part of the structure of the multiverse, and through strange hyperspatial physics, distances between locations are reduced in interstitial space; allowing for faster-than-light travel when compared to an equivalent journey between those same two points in normal space.

Appearance
Interstitial space is dominated by two monochrome planes - one red, and one blue, with a thin sliver of black between the two. Leading hypotheses, supported by readings of patterns in radiation emissions from these two planes and adjusted for Doppler shift, suggest that these two planes are actually our original universe, and our current universe.

Astrogation
Thanks to the constant radiation emissions present in interstitial space, combined with the lack of objects to act as reference, astrogation is nearly impossible without artificial reference points: either an extremely strong electromagnetic emission, such as those used to enable interstellar communication; or an exotic transmission method such as gravitational waves, neutrinos, or tachyons, which do not naturally occur within interstitial space.