The Dark Graveyard is a the prison Empress Quita and her followers were sealed in after the dark war, and now acts as their base of operations.
The Dark Graveyard is, well, a graveyard, apparently floating in space outside of the solar system. All of the rebels were turned into gravestones, each featuring a picture and the name of the being trapped on its face. Quita, her daughters, Haxlax and Gevlant's stones were larger than the others, and her husband's resembled a palace. The weather is typically stormy, and it has at least one tree.