Rura Penthe

Rura Penthe was a penal colony of the Klingon Empire located on an asteroid in the Beta Quadrant of the Milky Way Galaxy. Surface conditions were harsh and frozen, the actual colony was subterranean, where prisoners mined dilithium. The gulag had existed since at least the early 22nd century, and was known throughout the galaxy as "The Aliens' Graveyard." 

Prisoners who grievously misbehaved were exiled to the surface, where nothing could survive for long. A magnetic shield surrounded the colony and served as a transport inhibitor, preventing escape.