Go in through the west set of doors from the courtyard of Dire Maul. You really don't need to clear anything except a path if you have ever cleared DM before. The one exception could be the big tree guy right before the door where you use the crescent key for the first time in the instance (just to get around him). He's at the bottom of the ramp. 80's shouldn't have much trouble getting past most mobs without drawing aggro.

Once you're past that, you'll enter the big circular room.. Hug the right wall until you get to the next door. This will take you to the library where this quest point terminates.

If you're looking for the 700 quest achievement in Kalimdor, this is one more towards that goal.

You can actually just go straight into DM North and take the door in the south-west corner of the lower area and it will lead you straight to the quest turn-in. There's no mobs to fight at 80(maybe lower too) going this way.

Also, you can only turn in this quest once, so don't make the same mistake I did and buy a whole bunch of them trying to get rep, it won't work.