Not sure if it is a repost.
If you do the "Ironforge Airport" glitch you can also discover a tunnel which, when you exit it, drops you into the abyss. Firstly, before you turn towards the airport, you must follow the brown terrain ((where it is snow/brown)) You must go down a huge slope and turn east. Continue east until you git a little farmstead. In the farmstead there is a sign post saying "This way, that way, the other way" You need to go this way. follow the route and you should be at the tunnel!