| Don't tell me. The skull, the corny line, your name must be Bonehead right?|
The title of this article is conjectural.
The Dark Dimension is an alternate reality that is the home of Dormammu.
The Dark Dimension is a magical alternate reality.
Mordo stole the Wand of Watoomb from Doctor Strange and used it to open a portal to the Dark Dimension and bring Dormammu to Earth. However, in order for Dormammu to come to Earth he had to be accepted by a human. Dormammu pulled Mary Jane Watson into the Dark Dimension and tried to trick her into inviting him to Earth. However, Mary Jane saw through Dormammu's tricks and refused him access to Earth. This left Dormammu trapped in the Dark Dimension.
Sometime later Baron Mordo and Carnage were able to free Dormammu from the Dark Dimension by using the Inter-Dimensional Probe which was created by Stark Enterprises. Spider-Man managed to reverse the polarity of the probe which sucked Dormammu back into the Dark Dimension. However, Spider-Man discovered that Dormammu had created a link between Carnage and the portal. Venom sacrificed himself and sent himself and Carnage through the portal into the Dark Dimension. Spider-Man was then able to use the Inter-Dimensional Probe to close the portal.
Sometime later Venom and Carnage managed to escape the Dark Dimension through unknown means and they returned to Earth.
The sky in the Dark Dimension is green.
There appears to be no planet in this dimension. Instead several islands float in the air that Dormammu and other beings stand upon.
There are also waterfalls that appeared to magically fall from nowhere.
In the Dark Dimension there are also several large chains floating in the air.
In the comics
The Dark Dimension is a melding of alternate and abstract realities that were merged together into a single realm. The melding ended when the realm of the Mindless Ones was added in. Over many years there had been many rulers of the Dark Dimension including Olnar, the Wizard King, Umar, Clea, and Dormammu.