“‘Darco’ is slang for “De-Urbanized Arcological Construct”. Originally designed by the twisted genius of Dante McCallavre, the artist/architect proclaimed it a reactionary response to the rigid, archetypal Arcologies of his day. No one really knows what this means, and many engineers are frankly baffled at how the thing stays standing. Inside, the ill-lit corridor’s twist into odd, meandering corkscrews that mysteriously turn back on themselves. There are rumors that a strange sub-species of man inhabits the air ducts.”
— in-game info

(The other two kinds are the Plymouth Arcology and the Forest Arcology, BTW.)