Well so all what u need is Reins of the Traveler's Tundra Mammoth - Item - World of Warcraft to use this nice exploit.
To pass the first wall - >< - if uf stay like this just unmount now u will fall into the wall and can walk through it.
Now for the inner door we use this nice mount again look here - > < - if u stay like this just unmount again and u will fall into the door and u can walk throught it again.
And now if you are an rogue u can go there - > < - and if the door is down you can start to tap the orb and in 90% no one will interrupt you cause no1 will think that there is som1 before the door is down.
Feel free to ask if the pictures aren't informative enought hf with this