The Medium

The mysterious realm John's house was sent to when he bit into a Cruxite Apple. The other three children's houses will undoubtedly be sent here in time. Nannasprite describes The Medium as "a ring of pure void, dividing light and darkness" and mentions that it's part of The Incipisphere. The Medium seems to be the main body of the Incipisphere, with a kingdom of darkness below it relative to the four main planets and one of light above them.

The main goal of Sburb is to reach the Medium and build up to the Seven Gates, eventually reaching the Realm of Skaia at its center. A number of Shale Imps and Crude Ogres, and undoubtedly other opponents, exist here, the player having to fight them as they build upward.

It is likely that each for the four children will have their own planet from which they must reach Skaia. However, a diagram displayed by the Laboratory's primary session terminal seems to suggest that there are in fact eight planets, each with seven gates between it and Skaia. The significance of this is as yet unknown, these planets could be for trolls or antiheros

Strangely, players still receive electricity, while it seems nothing exists in the abyss below and the wires are clearly not connected to anything.