Shadows and Fire Dimension
The Shadows and Fire Dimension is a dark dimension full of exactly that, shadows and fire. It is so dark, in fact, that the only sources of light are the raging fires that spontaneously erupt around the dimension at random intervals.
This dimension was discovered by the Great Beings as early as 625 CMT (at the latest). It was here that they created the Elite Makuta and many of their alternate-universe counterparts, including the Blackouts that made up the Alternity.
When the Pandorica was activated in 150,080 CMT, Blackout teleported himself, Malygos, Zev, Ryoko, Washu, Tyrigosa, Anzu, Dr. Doppler, Misaki Raregroove and the Alternity to the Shadows and Fire Dimension to make them watch their universe burn from the other side of a portal. When Blackout and the Alternity left, however, the others chose to return to the OU through the portal in an attempt to stop him and the Pandorica.