Throughout Outer Heaven, you'll encounter numerous prisoners held in various cells. Rescuing these prisoners is highly beneficial. Each prisoner you rescue will provide you with either a Ration (restores health) or a piece of Intel (hints about item locations, enemy weaknesses, or plot details). Some prisoners even provide crucial Card Keys or other essential items.
To rescue a prisoner, simply approach their cell and open it with the appropriate Card Key. Once the cell is open, walk into the cell to trigger the rescue. The prisoner will then provide their reward. Be aware that some prisoners are in heavily guarded areas, requiring careful stealth or combat to reach them. Prioritize rescuing prisoners, especially if you are low on Rations or stuck on a particular puzzle.