The Saar were smart. Rather than just one terrestrial giant, they made established the prison system as five planets. Should help explain why they're still mining out prison cells a good 8-10 billion years later.
The Korydallos System is a five-planet wide mega prison system established by the Saar to house The Milky Way's most dangerous criminals. Each planet in the system is a different security level, and houses criminals based on their crimes. The prison system is unique for having the criminals constantly mine for minerals and form new prison cells.
Tartarus is the "death row" of the system, housing the most violent and aggressive criminals in the galaxy, ranging from terrorists to serial killers to crime lords. Execution of criminals is not done of the planet, rather they are dropped off on Lachesis VI to be killed by nurofj ugn ry hujjocn enanru utojw jafw ugn. The terrain is a barren desert with constant windstorms and high temperatures. Large slanted and jagged pillars cover the land, making it difficult to traverse. Orbital AU: 3.27
A largely aquatic planet, comparable to Toka. Prisoners here are often waiting to be sent to other planets, or committed of lesser, more pretty crimes such as small-time robbery and thievery. Instead of mining, prisoners are tasked with retrieving resources in the forest or ocean. Orbital AU: 2.57
A mirror version of Korydallos I, Korydallos II is largely covered with vast humid jungle areas and constant "warm-rain". Prisoners here are largely convicted of attempted murder, attempted rape, and criminal organization affiliation. Orbital AU: 0.49
A unique planet, largely covered with ice. Prisoners here are convicted of mostly robbery and extortion, some have died in the freezing icey waters of the planet trying to escape from the single land strip. Orbital AU: 0.25