Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150426193759/@comment-25177957-20150428204138

Actually, the C'tan known as the Outsider is trapped in a dyson sphere somewhere on the close fringes of, but outside the galaxy. No one knows who created this dyson sphere, where it is exactly, how old is it, or how it is inside, but it's possible the entire thing is now controlled by the Outsider. Dyson spheres are very rare in 40k, and the one containing the Outsider is the only true dyson sphere. Good point about the Dark Eldar though, Commorragh is technically a dyson sphere but in the webway considering it's size, and methods of collecting energy, also the Eldar Craftworlds might be considered a minature Dyson spehre, or atleast something similar to a O'Neill Cylinder with an artificial habitat.