The Municipal Library of Prague in the Czech Republic has an imposing cylindrical tower made up of 8,000 books that stretches from the floor to the ceiling. The tower is an art piece entitled “Idiom” by the Slovak artist Matej Kren. But even more remarkable is what you see when you peek through a 10 foot tear-shaped hole on the side of the tower.
This illusion is achieved by using two parallel mirrors: one in the floor and another in the ceiling. When a person walks in between parallel mirrors, the mirrors generate multiple images made up of reflections, reflections of reflections, and so on seemingly to infinity. However, some of the images will show the person looking forward and others will show the person looking backwards. In the case of the book tunnel, the surfaces reflecting on the mirrors are pretty much homogeneous, so the effect is created of a tunnel that stretches up and down to infinity!
The picture is by the author and can be used with permission.