The concept was a 30 foot long twisting corridor with faces covering the walls, for a section of Joker's Hideout. That seemed simple enough, make a ton of fiberglas faces, make a screen armature over the walls. Insert the faces through holes in the screen, secure into place, stucco over screen, paint. 

Well, that's more or less what happened, though an awful lot of improvizational engineering went along with it.I made over 160 faces from 12 molds from fiberglas & foam. 

I then went on site and stapled up chickenwire and screen armatures for this hellscape, and placed the heads in at varying angles to maximize the illusion.