Victims of Imprisonment - Baldur's Gate 2 Side Quest
The Victims of Imprisonment is a somewhat unmarked side quest involves the Spherical Prison in the central portion of the Underdark. When you approach this area for the first time there will be a group of Drow nearby but aside from this there is nothing else in the area to suggest that this object does anything of importance. The first 4 times I beat the game I had no idea this orb even existed, it wasn't until I started writing my walkthrough that I found it.
How this prison works is there are a total of 6 different facets that you can click on and each will release a different prisoner. To find these facets you should mouse over the Spherical Prison while zoomed in; specifically you'll want to loot for areas where the cursor changes to 2 arrows in a circle pointing to each other. For the most part finding all the facets is easy except for #1 and #6, they're on the edge and difficult to see and click.
Below is a complete list of all the prisoners you can release from this prison along with what items you'll get for defeating them.
Starting Left to Right Prisoner List:
1. Madman Aganalo: He attacks you no matter what you say. You'll get 6k EXP as well as Jhor the Bleeder +2 for defeating him.
2. Raevilin Strathi: At first Raevilin is very confused and attacks you and your group. There are 2 ways of solving this encounter, killing him will give you the far better reward of 20k EXP along with Conjure Earth Elemental Scroll and Summon Efreeti Scroll. If you cast Heal on him then you'll get Albruin +1 and 15k EXP.
4. Alchra Diagott: This prisoner is a Lich and is by far the hardest of the bunch; combat with this NPC is unavoidable. Defeating the Lich will earn you 22k EXP as well as Scrolls for Delayed Blast Fireball, Spell Turning and Summon Nishruu.
5. Bedlen Daglefodd: Bedlen is involved in the Svirfneblin Son Missing side quest which begins by speaking with a Svirfneblin in the village to the north. Follow the link provided for more information about this quest.
6. Gont of Riatavin: Out of all the facets on the prison this one is the hardest to click on since you can't even see it without mousing over it. Gont will not attack you when you summon him and you're able to let him go for no reward at all or fight him for 7000 EXP.
Once you've released all 6 prisoners from this prison you're done with the quest. Some of these NPCs will create an entry in your journal titled "Victims of Imprisonment" but there is no reward or overarching quest involving all of these NPCs. The one quest that involves this Spherical Prison is the Svirfneblin Son Missing side quest.