The Prison Island was an island which had training zones that were substantially better than the Main Island, Desert Island and Lost Sea Island. However, SS class was required to access the island and at least 10 Sp for the Strength, Endurance or Psychic stats respectively to train there.
As with all other game islands, the Prison Island had a chest called the Prison Chest which allowed players to collect 10,000 
every 7 hours.
An NPC clothed as a prison inmate was present inside the cell building (where the portal is located), which sold boosts for tokens (Boost Shop), limited to 5 for each boost each day (reset time at 00:00 UTC).
Prison Inmate
| Training Zones - Strength |
- The Prison Punching Bag (90B Strength Multiplier) - 10Sp Strength
- The Gun Cabinet (2.5T Strength Multiplier) - 5N Strength
| Training Zones - Endurance |
- Jail Cell (90B Endurance Multiplier) - 10Sp Endurance
- Swimming Pool (2.5T Endurance Multiplier) - 5N Endurance
| Training Zones - Psychic |
- Police Headquarters (90B Psychic Multiplier) - 10Sp Psychic
- Helicopter Pad (2.5T Psychic Multiplier) - 5N Psychic
| Trivia |
- The map of the Prison Island was based on the Mad City Prison Map
- On the desk inside the police station, there was a paper with a binary code on it, which translates to " Yes, this looks like the perfect place to begin our invasion..."
- As of Update 5.0, the Prison Island has been replaced with the Robot Island.