In this demonstration, students are challenged to determine the orientation of the cube, but their brains have a difficult time making a decision.
We use lines in objects for clues about depth. In the Wire Necker Cube, it is not clear which of the two vertical lines in the middle of the cube should be closer to you. Usually, we assume the longer line is the closer one and the shorter one is further away, but in this illusion the two lines are the same length.