You can see the back of the portal of Stratholme when you jump certain places on the side of SM and run all the way to behind Stratholme it's like an empty unfinished zone. Can also get inside an empty ZG.
SM to Strath: http://www.youtube.com/watch?v=Yk8v7MNmy_w
Please note if you get caught by a GM doing this it will lead to a ban. It's fun to know that it can be done but don't actually attempt it ;P