You heard me. It is possible to blink through the Stratholme backdoor instance portal on both sides.
You have to get close enough to blink to the other side, but far enough away to not get sucked in... takes some practice!!!
If you jump off by blinking through while inside the instance, you can fall underneath the instance. I am not sure what happens if you jump off from the outside non-instanced portion...
I don't know if this is doable in the main entrance. When I get time I will test other instances to see how many can be blinked through
Just a notch above an easter egg, one more place you can add to the list of places you can't normally get to!