Underdark Exit Overview - Baldur's Gate 2
As the name of this map suggests, you'll find the Underdark Exit here. Your first time leaving the Underdark you'll pass through this zone and be captured by a group of elves lead by Elhan. If at any point in the future you wish to return to the Underdark you can do so by traveling to this map and back into the same cave you exited from.
There is not much to note in this area except for Elhan's camp which you'll be visiting twice during Chapter 6 of the main story. Once when you leave the Underdark and a second time after you retrieve the Rhynn Lanthorn from Bodhi. The only other thing to note about this zone is your first time exiting it you'll encounter Drizzt on a small waylay map. You'll be able to ask Drizzt for help in the fight against Bodhi if you wish - you can also attack Drizzt if you want. However, unlike in BG1 where you could keep Drizzt's armor for the entire game, in this game an NPC named Malchor will eventually show up to take all of your Drizzt items if you kill him and take his stuff.
Elhan: Elhan is the leader of the elves in this area and an important NPC for the main story of this game. As I mentioned above you'll need to bring him the Rhynn Lanthorn during Chapter 6 so that he can open the path to Suldanessellar for you and your group.
Underdark Exit/Entrance: When you leave the Underdark for your first time you'll exit out of this cave and be captured by Elhan and his band. If you ever need to return to the Underdark in the future for any reason you can do so by traveling through this cave and back the way we came.