This is one of the toughest puzzles in the game. To ease you through,
here are some instructions.
First, note that the one who gives you the quest for this dungeon is
actually the Fire Lord himself, now nothing more than a face in the wall!
He will also reward you after the task is done.
In the hall you will find a lot of ambers. You need two of these to unward
the warded doors. In addition, if you give one amber to each character,
nobody will get hurt in case you have to ask one of the Stone Faces to
port you back to the entrance. Don't do that too often though, or you will
run out of ambers. If you have some left after the job is finished, you
can sell them for 500 gold in Free Haven.
This is what you need to do in the Hall of the Fire Lord:
 Speak with the face in the wall near te entrance, this is the Fire Lord,
who was real mighty in ancient times!
 Take the 4 ambers from the chests and give one to each of your party members.
 From the "top above the holes", jump into the south-east hole.
Make your way to the SE Chamber where you can find some chests with two
more ambers. Jump into the hole, and you enter the main hall.
Watch out! There is an entire army of goblins and ogres waiting for you!
 Find the hole on the east side of the main hall.
You will come to another jump down, with 3 ways: one deep jump in the
middle and two small corridors to your left (north) and right (south).
You will go here 3 times:
[4a] Jump into the deep central hole. You will meet a Fallen Defender,
kill him and take his key.
[4b] Jump right and take the corridor, it leads to a room that
teleports you to one of the four Chambers. There are other routes to
get there, but this one is easiest. In this Chamber you find a warded
door, use one amber to unward it.
[4c] Same deal after jumping left.
 Now that you have unwarded the two warded doors, in the NW and NE
Chambers, speak with the Fire Lord again to get your reward.
 Go to the "top above the holes" once more, and jump into the north
hole. At the end of your way you will find a chest. Save the game!
Have the character holding the Fallen Defender's key touch the chest on
the right side (seems to give better chances than the front). If the
chest explodes it won't open and the key is lost. In that case, reload
the saved game. Keep trying until you get it right, this is important!
Take the Crystal Skull, you will be glad to have it later in the game.
You can explore the rest of the Hall at your leasure, but there is little