A closer look

When you have limitless funds and the best artists of the Renaissance, you build architectural party tricks. St. Peter's Square is surrounded by massive colonnades that are four columns deep. However, Gian Lorenzo Bernini designed them with such absolute precision that if you stand on one of two specific marble discs in the plaza, the rows align perfectly, and the outer three columns magically vanish behind the first row. It's a 17th-century magic eye poster.