Known this for a while, but not posted. Now the 5er instance heroic bug is fixed, so its only usable as a mage.
Follow the screens, hope it isn't a repost.
To go behind the instance area, you should fill up the instance. Or as a Mage, blink exactly here:
There is an invisible wall, so you have to go around. Follow the way on the screens.
For this one, you have to try a while. You have to jump with your side ( with e or q ) ontop of thie fire thing. I don't know if it's possible for all classes, have only human mage, sorry.
A picture inside:
There i a way inside of uninstanced BRD, which is nearly complete black.
Hf