De'Arnise Keep Overview - Baldur's Gate 2
De'Arnise Keep is a location that you will visit during The De'Arnise Keep has been invaded side quest which begins by speaking with Nalia inside of the Copper Coronet, a bar in the Slums District of Athkatla. When you first arrive at this keep you will want to visit the small command tent in the bottom left of the map, this is where you'll find Captain Arat as well as the secret entrance to the keep.
Important: In order to "complete" this dungeon all you need to do is defeat TorGal, the leader of the trolls, in the basement. Once TorGal is defeated and you exit the keep you will lose all of the loot inside that you did not pick up. For this reason it's very important you make sure you get your Flail of the Ages +3, Elven Court Bow +3 and Frostreaver +3 from inside prior to doing this.
Note: I recommend you buy the Sword of Flame +1 from the Adventurer's Mart in Waukeen's Promenade before coming to this dungeon. This weapon will allow you to easily defeat trolls once they fall to the ground because you need to deal either Acid or Fire damage to permanently kill them. Having this weapon will make exploring this dungeon significantly easier.
Forge: This is where you can combine all 3 of the Flail Heads that you find throughout De'Arnise Keep. Doing this will reward you with Flail of the Ages +3, one of the best weapons in the entire game.
Flail Head (Cold): You will need this Flail Head as well as 3 others in order to craft Flail of the Ages +3. Where you find this Flail Head you'll also find Ring of Earth Control which gives +1 AC and stacks with most other protective gear.
Kitchen: If you defeat the dogs in the outside Courtyard area and collect all of the Dog Meat then you will be able to cook up some Dog Stew for 11,500 EXP; this is used to feed the Umber Hulks in the basement so you don't have to fight them. Keep in mind you can feed them + fight them so you can collect EXP from both.
Keep Key: You'll need this key to open many of the locked doors throughout the upper levels of De'Arnise Keep.
Flail Head (Fire): This Flail Head is located in the left-most statue in the treasure room. If you only take the Flail Head then none of the golems in the room will activate. When you take any of the other items in this room golems will activate to fight you. The Kneecapper +1, Elven Court Bow +3 and Frostreaver +3 are the other magical items that you can find in this room.
Lady Delcia: During The De'Arnise Keep has been invaded side quest you'll meet with and speak to Lady Delcia in this room. It's not required to talk to her to complete the quest.
Glaicus: Glaicus is charmed when you first enter this room and the ideal way of handling this fight is to use Dispel Magic on him or to Charm him yourself (which will break his charm). Charming or Dispelling Glaicus will get you 22k EXP as well as Flail Head (Acid). Killing Glaicus will get you 9.5k EXP and the Flail Head (Acid).
Umber Hulks: This is going to be the most difficult fight inside of the entire keep, assuming that you're low level when you first come here. In order to skip the Umber Hulks you can create Dog Stew using Dog Meat; defeat the dogs in the Courtyard and put their meat into the Kitchen stove. This will cook up some Dog Stew which you can then drop off at the specific location I show on the map above.
Dog Stew Location: If you want to distract the Umber Hulks with Dog Stew you'll have to use Invisibility on a character and sneak past the Umber Hulks. Place the Dog Stew at this location and then the Umber Hulks will rush over.
TorGal: TorGal is the troll leading the attack on De'Arnise Keep. Defeating this boss will end the troll invasion and complete The De'Arnise Keep has been invaded side quest.