The Covens of Corrobel are a series of Pocket Dimensions that don't obey the standard laws of physics.
The denizens of the Covens of Corrobel are the Naga, enormous serpents with the faces of men, who ruled over populations of primitive humanoids through a form of psionic hypnosis.
Following the rediscovery of the lost Mage Imperium colony vessel known as Witch Haven, its primarily psionic population spread slowly into the wider cosmos. Along the way, they brought whispers of strange worlds lying just beyond the Etheric Ley Lines, planets where the rules of reality appeared bent beyond mortal comprehension. These worlds, described as "covens" by the witch-folk, were known mostly through collective visions and, very rarely, trade visits.
In the last ten years, the stories from Witch Haven have been corroborated by intrepid etheric explorers, who have made contact with servants of the Naga and even seen the formidable creatures for themselves.