Grumborg Prison was a maximum security prison constructed by the Kortok on Brunk's moon, Grumborg. It was built by simply finding the largest canyon on the moon and sealing it over with a roof of solid steel; the Pokstone terrain practically guaranteed that no one would dig their way out.
Morbilus Grendy was sent to this prison for being a popular local leader and threatening the Kortok's power. He was rescued by Spuckler Boach, who got himself arrested on purpose, dug their way out with his trutanium leg, and hijacked a jet scooter back to the planet.
Following the overthrow of the Kortok, the prison was emptied and gradually fell into disrepair.