I just found a way underneath the Well Eternity, here is a picture for now, the next time I get well of eternity as a random heroic I will film how to do it.
Basically, if you are a rogue, you can either shadowstep or killing spree to mannoroth just as he is sucked over the invisible wall, then you will be teleported to his position and you are free to explore
Full size picture link: https://i.imgur.com/9AIKx.jpg