EDIT:WARNING: Paint Skills at work.
EDIT: Added The Suggestion by rebelsnowboard
Appologies: There are 10 pictures in the guide and it might take a bit to load...
I did a search for the Greymane Wall and the only returns I got were a few vague outdated guides.
Step 1
Go to 47,84 in Silverpine Forest
Step 2
Run over here to this larger tree that sets on the side of the hill.
Step 3
I would suggest to mount up just to quicken the process. Aim your character to partially be facing the mountain, hold down the run button and spam jump till you reach the ledge.
Step 4
Dismount and run to the little crack in the wall here, jump into it.
Step 5
Walk along the edge and up the wall to the top behind the tree.
Step 6
This part requires you to either be a mage and use blink, or to delete your Hearthstone and use the Auto-Unstuck feature. Use it while your nose is pressed against the invisible wall.
*note: you dont need to delete ur Hearth just make sure it isnt on CD when you use auto-unstuck and it will work as if you dont have one.
Step 7
Mount up and jump to point labeled in the picture. if you fall short just get up and try again or you may try jumping up the corner where the wall and the ground meet.
Step 8
Now you must face the wall with your back to the incline of the hill. Be at about a 45 degree angle with the wall. Now just run backwards and jump. This should only take about eight or so jumps.
Step 9
You have almost made it just jump down...
Final
Have Fun!
Enjoy this guide, I believe it will be able to help anyone who would like to get behind the Greymane Wall and explore all of its wonder!... <3