Well i was flying around in orebor harborage in zangaramarsh when i sudenly saw a smal hole behind the inn. i fly trough it and i could fly underneath the ground. watch out from water , you wil be diss mounted if you fly there.
Here are some screen shots
ImageShack - Hosting :: wowscrnshot123107024014qg5.jpg
ImageShack - Hosting :: wowscrnshot123107024024pg7.jpg
I dont know if this has ben posted before.
GL flying around under the world :P