There is an arch way across from you cleanse yourself when you're infected and in this archway or tunnel you're going to want to be on the left side of the arch if you're standing by the cleanse area. Head into that tunnel there and you're going to want to crouch right where I am in the video. Its the 3rd to last steel plating on the left side if you enter the glitch spot from where I did. Once you're there zombies will come up to you but can't really damage you or hurt you. There are the spike zombies where if you shoot them they ricochet your shots at you.