My take on the facade of San Lorenzo, the Medici family parish church and originally the primary cathedral for the city of Florence.
The facade is one of the most famous unfinished structures in Italy. The church was designed by Brunelleschi, but he died before it was completed. The Medici family, who were financing the construction of the church, commissioned Michelangelo to design a new facade. He built a scale model, but the design was never executed. In 2009, a CGI model of his design was projected on the existing facade for a period of time to gauge reaction to completing the facade, but nothing more has come of it. While the Michelangelo design is quite beautiful, the current facade has sat as-is for over 500 years, so I think it would be a sacrilege to both the existing building and the Michelangelo design to build it now.