All there is is just pavement in front of him, and the street below together with the crowd, plus the building below him on fire, are all tricks played on the eye. It is also the angle that it has been taken at to make the illusion more effective. At first the impression that it gives you is that it seems to be real but then quickly you notice that it is actualy just an illusion due to the fact that what you are seeing is not really possible. At times it acts as a metaphor on how we see things wrong because the brain makes a wrong interpretations, so we see things differently from the actual reality. Taking this from another angle there will be no optical illusion as it may not even make anysense of what is actually there.
We see with our brain and not only with our eyes. When an image falls onto the retina, nerve impulses are sent to the brain where the actual perception takes place. The brain puts together bits and pieces of information, matches the vision we see with our eyes with the images stored in our visual memory, so that we know what the object is, and interpret visuals so that we know where the object is.