Three-dimensional illusions of Kurt Wenner

The new book presents a selection of outdoor three-dimensional illusions of Kurt Wenner,
 a former employee of NASA, which uses math skills to create
 three-dimensional illusions on sidewalks around the world. When viewed from the correct angle
 it seems that the people behind them, flying in the air, and in-situ concrete can
 It looks like a bottomless pit. Kurt perfecting his technique since 1982.