The Dimensional Gap (次元の狭間 Jigen no Hazama) is a location that lies between the different worlds of High School DxD.
The Dimensional Gap is the gap that exists between the three worlds (Earth, Heaven, and the Underworld) and is considered a void world. The Khaos Brigade uses the Dimensional Gap as a means of traveling. It is the birthplace of Ophis, the Infinite Dragon God, and Great Red, the True Dragon. The Dimensional Gap was originally the home of Ophis and is currently being occupied by Great Red.
Floating within the Dimensional Gap are the Gogmagog, Golems created and later abandoned by the Ancient Gods. Aside from the one recovered by the Vali Team, all of them are inactive.
Nothing can survive within the Dimensional Gap without magical protection. Anyone without such protection dies within a matter of seconds after being exposed to the "nothingness" within the Gap.
The Dimensional Gap is an endless void, where in every direction, there is a mix of iridescent colors. In Volume 12 Issei Hyoudou describes it as "looking through a kaleidoscope."