A place which is part of, and just “outside” The Hub.
It is a black void with an antipodal blue glow. There is no atmosphere here at all. No sound can travel, no heat or warmth can be conducted or radiated.
This is where ships pass during a Transit.
The time spent within Hubspace is relatively brief. Calculations for the exit point are made before entering. There has never been an incident where a ship was stranded in Hubspace itself. If there is some kind of failure within the Artikybahl Device during the transit, the ship is returned to the Fifth Realm at the point of origin.
Note: Despite operating on the same “technology,” Inter-Realm Constructs cannot reach Hubspace itself. If they delve deeply enough, they will emerge into the Hub itself.