Instructions
Go to the portal in front of Stratholme. This is the portal you use to enter the instanced area. Stratholme is predominately used as an instanced dungeon. Each party enters a separate copy of Stratholme upon entering the portal. Do not enter the portal.
Go right until you see the corner formed by the wall of Stratholme and the surrounding mountains.
Walk into the corner. Eventually, you end up walking up onto the small ledge at the base of the wall.
Walk along the ledge until you are standing in the corner just to the right of the portal.
Walk into the corner until your character appears to be jumping, despite still being on the ground.
Summon any mount. Summoning the mount should cause you to go through the wall if you are in the correct space. It may take a couple of tries to get this step to work. It should appear as though there is nothing below you, except water.
Walk straight to start falling. You fall into a non-instanced version of the Stratholme dungeon before you hit the water. There are no enemies or NPCs here, unlike the instanced version of the dungeon.
Walk straight down the road until you see an archway that has a completely red opening. This is straight in front of your path.
Go through the red opening. This takes you to the area behind Stratholme. There is nothing here, but you can see you are in the correct area if you look at the world map.