High Garendall is the area far far to the north. You need to enter a temple that is
guarded on the outside by dark wraiths(they look like shadows) and on the inside by
ghouls. When you exit the temple you will be on the same screen as you were before, but
on the other side of a cliff. Head east and north and you will eventually cross a
narrow bridge that is just to the east of a gigantic stone giant. Heading north
across this bridge will deposit you into High Garendall where you can finish the
Standard quest and the Tome of Elixirs quest.
To enter the temple that leads to H.G. you must have an access key found on the 3rd level
of the learning tree. If you haven't made it to lvl 3 of the tree, you need to gain
access first.
One note: On the area that has the temples(you enter/exit them to get past the
chasm and hence into H.G.), there is also a cave in the northwestern corner. This
does NOT lead to High Garendall. Do not go there until you have the guardian quest.
Well, you can if you want to, but there is a gate at the bottom that will not be
enterable until you have the above quest. H.G. is to the east and north of the temple
and not through the cave.
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Shoot 'em with everything you've got. If anything still lives, shoot 'em again.