Vaal Ruins in Delve?

Found a vaal ruins in Delve (like vaal zone). I entered it and at first all was good but suddenly the darkness started to deal damage out of nowere. The problem is a player doesn't know what is waiting ahead so he could prepare somehow . Losing experience for nothing is no fun.

The entrance should be fine in the ruins. You need to stand on those red circles to get stuff to light up :) (worked for me anyways)