Lavok's Sphere, also known as the Planar Sphere and referred to almost exclusively by that moniker, is a massive and wondrous piece of arcane engineering that appears in Baldur's Gate II: Shadows of Amn.
The Planar Sphere is a magic-crafted fortress, possibly a self-contained Demiplane, which is also capable of planeshifting at will to other places throughout the multiverse. It is even capable of travelling to other worlds scattered across the Prime Material, even those that are normally "sealed" against incursions, like Athas and Krynn. It derives this power from an arcane engine that apparently consumes the hearts of Outsiders as fuel; it is unknown if it requires Tanari'ri hearts specifically, or if other Outsiders, such as Baatezu, Eladrin and Aasimon, can also serve as fuel.
Created centuries ago by the wizard Lavok, for whatever reason, the Planar Sphere has recently reappeared in Faerûn, manifesting in the Slums District of Athkatla. The Cowled Wizards have been unable to breach its exterior, but divinations have revealed that the blood of a descendant of Lavok would open the Sphere and allow access.
The Planar Sphere is the dungeon associated with the quest The Hunt for Corthala Valygar, and cannot be accessed unless the party either includes Valygar Corthala as a party member or has Valygar's Body as an item.
As a DungeonEdit
The Entrance HallEdit
This is where the party enters the Sphere. It is a nondescript room that has three doors; the Guardian's Chamber to the west, the Welcome Room to the northwest, and the Viewing Room to the northeast. The Sitting Room is initially locked.
The Viewing RoomEdit
A magical pool here provides a view of the Sphere's immediate surroundings. There is nothing of interest here, though a Steam Mephit has gotten into this room and will need to be slain.
The Guardian's ChamberEdit
The first line of defence for the Sphere is the intruder-slaying Clay Golem that resides in this room. Once killed, its treasures may be taken. Scrolls of Breach, Haste, Polymorph Other, Minor Spell Turning and Conjure Lesser Air Elemental, some Arrows +2, some Bullets +2, some Bolts +2, and three key items may be found here; a Golem Arm and Coal, needed for a sub-quest, and the Planar Key, without which the party cannot proceed.
The Welcome RoomEdit
The first time the party enters this room, they feel the Sphere shudder and lurch; they have triggered an anti-intruder mechanism, causing the Sphere to planeshift away from Athkatla! Trapped inside the Sphere, they must press on. This chamber, a safe haven, contains three people in a similar situation; Reyna, Onvo and Anca. Talking to them will reveal they are Knights of Solamnia, a holy order of Paladins, Fighters and Fighter/Clerics from the world of Krynn, who have been stranded here ever since Lavok visited their homeworld and they investigated his Sphere. They will provide some valuable information about the Sphere.
To the north of the Welcome Room lies the Aquatic Room, whilst the west wall has a door to the Caverns.
There is a Scroll of Khelben's Warding Whip on the table here.
This is one of the rooms in which the party can Rest whilst they are trapped in the Sphere.
The Aquatic RoomEdit
A sea-themed chamber in which a Sahuagin Baron, a Sahuagin Priestess, and a number of normal Sahuagin have been imprisoned for purposes unknown. They attack on sight. When slain, there are Paralytic Bolts, Bolts +1 and a Cloak of Protection +1 to be retrieved here.
These dry, rocky chambers house a small village inhabited by halflings. Unfortunately for the party, these are not the friendly halflings of Faerun, but savage, vicious, cannibal halflings from Athas. The party will need to fight a number of low-level Halfling Warriors in the first chamber, then follow it around to the northwest, where they will enncounter the four leaders of the village; Togan and Kayardi, fighters much higher in level than their followers, as well as Entu and Mogadish, a halfling mage and priest duo. These two are particularly dangerous casters for a low-levelled or unprepared party, capable of casting spells like Chain Lightning, Flesh to Stone and True Sight, which they all have on by default.
The Caverns lead north and exit into the Golem Laboratory.
The Golem LaboratoryEdit
The party will be attacked by a number of Phase Spiders and Ettercaps when they enter this chamber.
This chamber is where Lavok builds his various golems, and a powerful one is currently under completion. However, it still needs its head and one arm before it can be completed. Exploring the room will turn up some Darts of Wounding, the third batch of Coal, and Lavok's Tome, which explains the purpose of this room and the golem within, and how to activate it; once its body is completed, the Furnaces to the north must be activated to empower it.
The purpose of this golem is as a defender of the Sphere against hostile intruders. As such, though it ignores the party, it will race off to confront the Elder Orb that has taken up residence in the Bastion. Activating the golem rewards the party with 23500 EXP; those who carefully partake in the ensuing battle can also potentially win the 14000 EXP for killing the Elder Orb, even as it ineffectively focuses on killing the unkillable Golem.
This room exits north to the Furnaces and east to the Rune Room. Be warned; there is a trap set in the eastern corridor.
A room containing three enchanted furnaces that are used to power the Golem Laboratory. All three have burned low and need Coal to be reignited. However, each Furnace that is restored will also spawn a Fire Elemental as a one-time event, forcing the party to face three Fire Elementals in total. The room also has some halfling warriors from the Caverns hiding in it, including two named ones - Taibela and Necre - as well as common grunts. One of the named halfling warriors drops the Stilleto of Demarchess, a Dagger +2.
This room exits east to the Clock Room and south to the Golem Laboratory.
The Clock RoomEdit
Presumably serving some purpose for the eldritch machinery that powers the Planar Sphere, this chamber is guarded by a number of Stone Golems. The center of the room has a container holding a Golem Head, some Arrows of Piercing, and more Coal, just in case the party missed one of the three sets earlier on. This room exits west to the Furnaces and south to a chamber interlinking the Rune Room and the Bastion.
The Rune RoomEdit
This room is dominated by four large runic designs on the floor, which seem to be feeding arcane power into a huge orb of energy-washed obsidian suspended in the center of the room. This setup creates a defensive seal around the stairway leading to the heart of the Sphere, and must be counterspelled to access the depths. Activating the runes in the right order will deactivate the wards; activating the wrong rune will blast whoever touched it with a Flame Strike spell and reset the puzzle.
The correct order to activate the runes is: Top, Bottom, Right, Left. Or: Northeast, Southwest, Southeast, Northwest, if one wishes to look at it like a compass. Completing the puzzle awards the party with 24500 EXP and grants access to the Sphere Core via the stairway to the South.
Heading east from the Rune Room leads to a corridor that can take the party back west to the Rune Room, north to the Clock Room, or east to the Bastion.
This chamber holds a doorway in the east leading to the Navigator's Room. However, an Elder Orb has taken up living here, and it makes for a fearsome battle. It is much easier to unleash the Guardian Golem upon it than to try and tackle it singlehandedly. Once it is dead, though, the way to Lavok is open. Search the ground carefully; a hidden cache contains Scrolls of Spell Thrust and Breach.
Heading west leads to a corridor that can take the party to the Rune Room (west), Clock Room (north) or Bastion (back east). A door to the east leads to the Navigator's Room.
In this chamber, Lavok directs the path of the Planar Sphere. Angered by your besieging of his home, the malevolent wizard attacks the party. He is a difficult battle, being high enough that he can cast spells like the lethal Abi-Dalzim's Horrid Wilting.
Once defeated, Lavok, mortally wounded, regains his senses, and explains to the party that only he has a chance of returning the Sphere back to Athkatla, begging them to let him go home and see the sun of his birth-world one last time before he dies. As the alternative is being stranded in the Sphere, which he warns is currently stuck on a layer of the Abyss, for the rest of their lives, the party must agree. Lavok explains that the Sphere has exhausted its power, and needs the heart of a powerful Tanar'ri as a fuel source. As they have landed in the Abyss, it shouldn't be too hard to find one.
Once the party has repowered the Engine, they must return here. Lavok will return the Sphere to Athkatla, draining the power of the Engine entirely to do so, and then plead with the party to let him feel the sunlight before he dies. If they refuse, he gives up and dies, leaving the quest complete. If his wish is granted, he dies gratefully, awarding them with 45500 EXP and his Ring of Acuity.
The confrontation with Lavok goes differently depending on whether or not Valygar is in the party.
This room connects to the Bastion by a door in the south, to the Mushroom Grove by a door to the east, and to the Tech Room by a door to the north.
The Mushroom GroveEdit
Presumably a source of food for Lavok and any others he deigns to share it with, this chamber of lush greenery is protected by two Spore Colonies, which produce Myconic guardians to attack intruders - like the party. If they are slain, a Sling +2, a Quarterstaff +1, some Bullets +1 and some Potions of Extra Healing can be found secreted in the treetrunk. Return to the Navigator's Room by a door in the south.
The Tech RoomEdit
The purpose of this chamber is unknown, possibly it's Lavok's sleeping quarters. Three angry Lizard Men will attack the party if they enter this chamber. There is a suit of (the "Protector of the Second"), a Ninja-To +1 and a Battle Axe +1, some Darts +1 and some Bolts of Lightning. Return to the Navigator's Room by a door in the south.
The Abyssal LayerEdit
Once Lavok has been defeated, he unlocks the door in the main room, allowing the party to explore the Abyssal Layer they have landed on. Imps, Salamanders, Fire Mephits and Maurezhi abound, but the party wants to kill at least one of the True Tanar'ri here. There are two True Tanar'ri roaming the area, worth 10000 EXP each, as well as a named True Tanari'ri, Lea'Liyl, who is worth 16000 EXP. Once the party has at least one Demon Heart in their inventory, they can return to the Planar Sphere, which is in the south-southeast corner of the map, and head to the Sphere Core.
This large hallway is entered from the Rune Room, by a door in the southwest. Doors in the northwest and northeast lead to the Ice Room and the Flame Room respectively.
A Cowled Wizard named Tolgerias and his assistant, a lesser Mage, managed to stowaway aboard the Sphere before it planeshifted away from Faerun. Unreasonably, the two of them attack the party and must be slain. They drop a Ring of the Ram.
The Ice RoomEdit
In addition to the number of traps scattered around this chamber, it also includes an Ice Salamander, as well as a number of Ice Mephits and Snow Trolls. The center of the room hides a cache containing some Ice Arrows and Fire Arrows, as well as a Helm of Defense and a Scroll of Otiluke's Resilient Sphere.
A door to the southeast leads to the Sphere Core, a door to the northeast leads to the Planar Sphere Engine.
The Flame RoomEdit
In addition to the number of traps scattered around this chamber, it also includes a Greater Fire Elemental, an Efreeti, a Salamander, and some Smoke and Fire Mephits. The central container has a cache of goods; a Staff of Fire, a a Shield of the Falling Stars (Large Shield +1, +4 vs. Missiles), Arrows of Fire, and Scrolls of Spirit Armor and Globe of Invulnerability.
A door to the southwest leads to the Sphere Core, a door to the northwest leads to the Planar Sphere Engine.
The Planar Sphere EngineEdit
This room powers the potent magics of the Planar Sphere. Only by feeding this bizarre machinery a Demon Heart can the Sphere return to Faerun. But first, the party will need to overcome its defenders; four Stone Golems, two Adamantite Golems, and a Clay Golem all roam this chamber.
In the northeast corner, a trapped container hides a, Ring of Danger Sense, 6666 gold pieces, and an assortment of gems.
Feeding the Engine awards the party with 45500 EXP and allows them to return to their homeworld, once they inform Lavok.
A doorway in the southeast leads to the Flame Room, a doorway in the southwest leads to the Ice Room.
As a StrongholdEdit
Once the Planar Sphere has returned to Athkatla, the Cowled Wizards are willing to grant ownership of it to Gorion's Ward if they are a Mage, Specialist Mage or Sorcerer - providing they are willing to prove responsible (read: "toe the line"). This begins a questline: Claiming the Sphere.
Unlike some Strongholds, the Planar Sphere provides no financial support. It's simply a show of status, and a source of experience whilst undertaking the quest. However, if the player ensured that all of their apprentices survived the training process, then one of them, Morul, will return to the Sphere and ask to stay on as the player's apprentice. Accepting means that Morul will randomly produce one of four sets of potions every week, which can be used or sold as the player sees fit.