Im not sure if this is a repost, but this is how i do it.
Get ontop of the barrel, (This is by the bank in gadgetzan)
Next, mount up.
Jump onto the red spot, it takes practice but you get the hang of it.
Jump and hold W at the same time, you should make it, move yourself with the right button on your mouse.
Once your on the roof, you need to run off of the roof on the little extra block extension, once you are on it (while running) jump and dont press any buttons. You will land on the wall if u jumped correctly. once again you get the hang of it fast.
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Once your onto the wall, walk toward the horde FP master. you will run into this. Simply Jump onto it, and keep yourself aimed toward the middle and "W" Around, and on most of them u can jump ontop of the spike and just jump to the next wall segment.
You should be heading this direction. just continue until you get.. to..
Here! Sometimes u can wallclimb onto the side of the wall next to the gate to get to the tippie-top. But it is ridiculously aggrovating.
SO Enjoy and /wave at nublets!