Before continuing, I would just like to note that this is not the spawn out of bounds glitch that’s been reported numerous times already. This is a glitch that allows you to get out of bounds in Nilgarf Sewers using a hole in the map itself.
You must be either a Mage with a decent investment in Blink or a Hunter with Double Jump.
To find the hole, first head to this location in the bottom layer of the sewers.
From there, face away from the fence and look forward and right and you’ll see something like this:
Head towards there until you reach this patch of land:
From there, go left and you’ll enter this area:
Continue through the left tunnel until you reach this “intersection” (which is normally a dead end on the right).
Rather than go left (like you’re supposed to), head right and look up. You’ll find a small hole in the ceiling.
From here simply follow the path up and out and you’ll be outside of the sewers (you can see the night sky on the right of this image):
As a side note, after exploring a bit I found a skeleton down here!