Someone previously posted a thread on being able to get under outlands by flying into a corner in the northern part of the aldor rise. I find it easiest to fly under shat as a druid because you can shift in and out of bird form and not worry about dying.
Fun part, as you fly under outlands, you are able to see people as they are questing. I found myself going through terrokar and hellfire and finding unsuspecting victims6):. When the time is right emerge from the earth and destroy them
Other classes can do this as well, but you have to be sure that you watch out for lakes and rivers or you will be dismounted and end up falling to a spirit res death.
huzzah!