You need to get the form whose ability it is to go through grid like fences like the one that locks the way to the northern part.
Those form is link to the quest "Sewer Investigation" that will be unlocked at the guild once you have enough reputation (I think 100 or 125.)
Hope that helps^^
Thats the plan.
I plan to add a permanent version in the full game that can be acquired later in the game^^