Hello.
Here is my guide for how to get inside uninstanced Stratholme.
I did it with mage, but I think you can do it with a Druid's "Displacer Beast" ability.
Link to the video
As you can see in the video all I do is fly up to the invisible wall and use Blink, you have to make sure you are close enough to the rooftop.
After that I just Slowfall my way down to the ground.
Note: You need to have "Auto Dismount in Flight" on, you can find it in the Controls setting in Interface options.
Note: This can pass through most invisible walls.
Written guide:
Go to the summoning stone for Stratholme.
Mount up your flying mount.
Fly up till you hit the invisible wall.
Place yourself so that when you Blink/Displacer Beast you will land on the rooftop.
Go down into Stratholme.