Inside the Planar Sphere - Baldur's Gate 2 Side Quest
Inside the Planar Sphere is the main quest associated with the Planar Sphere dungeon in the Slums District of Athkatla. To gain access to this dungeon you will need Valygar in your party or his body in your inventory. You can find Valygar in the Umar Hills map, he's located in a small cabin in the northern portion of this zone.
For more information about Valygar and where to find him I recommend you check out The Hunt for Valygar Corthala side quest, these two quests are closely related since they both revolve around Valygar. It's worth noting that you can have Valygar in your party just long enough to open the doors of the Planar Sphere then kick him out. You're not required to do this dungeon with him (or his body) in your inventory the entire time.
Our first task inside the Planar Sphere is going to be loot the Planar Key from the chest in the southern room near the front door and use it on the locked door leading deeper into the sphere. You will also find a Golem Arm and Coal in this room which are key items for this dungeon.
Inside the room you will also find a golem who is immune to all types of damage except crushing. Get used to this as there will be many golems throughout this dungeon (and the game) who can only be damaged with crushing damage. If you don't have a weapon that deals crushing damage I recommend you visit the De'Arnise Keep and obtain the Flail of Ages item. This is a best in slot weapon that you'll be using the entire game.
Warning: When you use the Planar Key on the locked door your screen will shake and you'll be locked inside this dungeon until you complete it. Make sure you are absolutely ready before proceeding with the rest of this dungeon.
The first room you come across in the Planar Sphere will have a group of knights that will tell you a little bit about what to expect. North of these knights is a room full of Sahuagin which will drop Cloak of Protection +1 along with some magical bolts. East you'll find a couple groups of very angry Halflings who can be difficult if you're under prepared.
Not very far into the cavern you'll find a Halfling named Togan who will run off when you get close enough to him. I strongly urge you not to chase after him as it'll likely result in your death. What you should do instead is throw a bunch of AoE spells in the direction he ran to blow up him and his friends.
After you defeat the Halflings make sure you loot the Gauntlets of Ogre Power and Coal from the ground. This is one of the best in slot gauntlets you can get in the game and is also used in the Cromwell's Blacksmith quest to create Crom Faeyr (another best in slot item). Now, as for the next things we need to do in the Planar Sphere... I am going to break it down into 2 parts.
Below you will find a step by step quick list explaining exactly what you need to do in order to finish this quest. For those of you who don't need your hand held the entire time you'll probably prefer this quick list. If you find yourself confused or stuck on any part of this quest then scroll down this page a bit further and I will explain each of these steps in much more detail.
Step-By-Step List of How to Complete the Planar Sphere:
1. Loot the Golem Arm, Coal & Planar Key then proceed into the dungeon
2. Defeat the Halflings and loot the Coal they drop
3. Obtain the Coal and the Golem Head from the northern most room
4. Use 3 Coal that you've picked up so far on the Furnaces in the Furnace Room
5. Place the Golem Arm & Golem Head into the Golem Forge to create a Golem
6. Follow the Golem east to the Navigator's Room
7. Defeat then talk to Lavok inside the Navigator's Room
8. Complete the Rune Puzzle on Level 1 to gain access to Level 2
9. Exit the Planar Sphere so that you're in The Abyss
10. Kill a powerful demon in The Abyss for a Demon Heart then return to the Planar Sphere
11. Use the Demon Heart on the Power Core on Level 3 to return to Athkatla
12. Carry Lavok outside of the Planar Sphere to complete the quest
In order to advance the quest forward what we need to do is light the 3 furnaces in the Furnace Room and then build a golem in the Golem Forge room. To ignite the furnaces you'll have to collect at least 3 of the Coal items from around the Planar Sphere. With the Coal in your inventory simply click on the furnace to summon a Fire Elemental then fight defeat it. Do this to all 3 furnaces to complete this task.
As for building a golem, you'll have to collect the Golem Head and Golem Arm from different rooms on the 1st floor of the Planar Sphere. If you need help finding the locations of any of the items that I mention, I recommend you check out my Planar Sphere Overview guide. Once you have both of the parts required to make the golem simply interact with the Golem Forge to create it.
The Golem you make will bust open the 2 doors leading east and give you access to the rest of this dungeon. Follow the golem and help it fight the Elder Orb that it engages - if you're lucky then you'll get the killing blow and the EXP for the enemy. Regardless, head through the door nearby and you will find the Navigator's Room.
You will find Lavok in the Navigator's Room and there will be some dialogue with him along with a somewhat easy fight. After the fight is over Lavok will ask you to help him, he wants to die under the Athkatla sky but right now the Planar Sphere is still in The Abyss. What we need to do is enter The Abyss and obtain a Demon Heart from one of the powerful demons here. This item will allow us to travel back to Athkatla to complete this quest.
In order to enter The Abyss you will want to exit the Planar Sphere through the same door we entered from; instead of ending up in Athkatla you'll find yourself in The Abyss. This is because when we first entered the Planar Sphere and used the Planar Key on the door (if you remember the screen shook a little and you got a short scene when this happened) we actually moved the Planar Sphere from Athkatla to The Abyss.
All we need from The Abyss is a single Demon Heart which only drops from the more powerful demons in the area. If you need help locating any of these demons I recommend you take a look at my screenshot below, it's an overhead map view of this zone with the locations of all 3 demons marked on it.
Map of The Abyss
Each of the 3 demons will drop a Demon Heart so it doesn't matter which one you defeat. Though I would recommend taking out all 3 so that you can maximize the amount of EXP earned in this area. Once you've obtained the Demon Heart you'll want to visit the 3rd floor of the Planar Sphere which is where you will find the Power Core.
First, we need to visit the 2nd floor before we can reach the 3rd floor (duh). In order to reach the 2nd floor you will have to solve an easy Rune Puzzle, a picture of what I am talking about can be found below. Essentially all you have to do is click on the runes in the correct order and this will open the door leading to the next floor.
The correct order is: North, South, East and West
On the 2nd floor you will run into Tolgerias who is a Cowled Wizard and also the person who started The Hunt for Valygar Corthala side quest (if you picked it up earlier). No matter what you say to him you'll have to fight Tolgerias and one of his mage allies. He'll drop a Ring of the Ram which is a decent clicky ring but nothing else of value.
You can find 2 other rooms on the 2nd floor, each of them will have a container in the center of the room that has some loot inside. Be sure to grab everything in both of them before proceeding to the 3rd floor. If you'd like a more detailed explanation of floors 2 and 3 along with the loot that can be found on them check out my Planar Sphere Overview page.
The 3rd floor is where you can find the Power Core which is the final step of the puzzle. With the Demon Heart in your inventory all you have to do is left click on the Power Core a few times to send the Planar Sphere back to Athkatla. On this floor you will also find various golem enemies which can be challenging depending on your group. Much like all of the other golems throughout the compound some of these can only be damaged with crushing damage.
After returning the Planar Sphere to Athkatla all you need to do is exit it to complete the quest. There will be a quick scene with Lavok after which he'll die and you will be able to pick up all of his belongings which includes a Ring of Acuity. Last but not least if you are playing a mage class and you don't own any other strongholds currently then Lavok will give you the Planar Sphere upon his death. For more information about the Mage Stronghold Quests follow the link provided.