Incipisphere

The Incipisphere is the bizarre universe that Sburb transports things to. It is structured as follows:

The Medium
The Medium is the space John Egbert's house was transported to. It is almost certain that if Rose, Dave and GG activate their Sburb Clients, their houses will be transported here as well. Things here are more or less like they were in Earth, except not: Shadows are darker, electricity is summoned out of nowhere, and Imps roam the area. Ogres can climb from realms beneath to harass creatures here.

The Dark and Light Kingdoms
Somewhere deep below the Medium, concealed by roiling clouds, are four Dark Spires presiding over a kingdom of darkness. One of these was activated by John's Kernelsprite's Dark Kernel when he was transferred, and now is aligned to Jesters.

Above the Medium, and presumably, above Skaia as well, four Light Spires adorn a kingdom of light. One of these was activated by John's Kernelsprite's Light Kernel when he was transferred, and now is aligned to Jesters.

The Seven Gates
The Seven Gates are arranged above John's house in a vertical fashion. The goal of the Sburb player is to build up to these one by one, and solve the Ultimate Riddle.

Skaia
Skaia is a "dormant crucible of unlimited creative potential" that lies above the Seven Gates. The kingdoms of the Dark and Light Spires are fighting for possession of this.