Inter-Realm Spaces are spaces between multi-realms. These spaces are even darker than Nothing or The Shadow Realm, and are very, very big. They make it so that The Multi-Realm doesn't collide with other similar Multi Realms.
When one Nothing is entered the thing that entered will be thrust into a completely white spacetime rift for 8,559,001 to 102,334,657 years. During this time they will not have any water, food, or air.