Found by Abystus
Trick is to go around to the left side of the instance (ouside the actual building. Now you will see a rock that is right next to the wall. At a certain angle you can walk up this rock and jump onto the wall and walk till you are to the left of the instance itself but on the same wall as the instance portal. Mount up and jump to the most left section infront of you over the wall and land on the rock on the other side. You are now in the instance, but if you get infront of the portal way you will be teleported into the real instance (you dont have to be next to it for it to teleport ya). If you ride your mount straight from the rock (basically along the wall all the way up to where you hit the first on the left of the instance) up the road deeper into the instance you will be able to dismount and run around the entire instance, tho you arent really in it. There are no mobs there, no chests, no nothing, but the whole instance is there without actually teleporting into it through the portal. At any time you would like to leave the empty instance just run back towards the portal and walk through and you will be teleported into the (actual) instance that is filled with mobs, then just go through the portal again to get outside.
Trick is to go around to the left side of the instance (ouside the actual building. Now you will see a rock that is right next to the wall. At a certain angle you can walk up this rock and jump onto the wall and walk till you are to the left of the instance itself but on the same wall as the instance portal. Mount up and jump to the most left section infront of you over the wall and land on the rock on the other side. You are now in the instance, but if you get infront of the portal way you will be teleported into the real instance (you dont have to be next to it for it to teleport ya). If you ride your mount straight from the rock (basically along the wall all the way up to where you hit the first on the left of the instance) up the road deeper into the instance you will be able to dismount and run around the entire instance, tho you arent really in it. There are no mobs there, no chests, no nothing, but the whole instance is there without actually teleporting into it through the portal. At any time you would like to leave the empty instance just run back towards the portal and walk through and you will be teleported into the (actual) instance that is filled with mobs, then just go through the portal again to get outside.