One of the most beautiful cathedral exteriors in all of Europe is arguably that of the duomo of Florence, Santa Maria del Fiore. Not only the facade of course, but the entire exterior is a marvel to behold, utilizing multiple colours of marble to create a kaleidoscope of form and colour. This particular building saw construction commenced in the year 1296, with the bulk of the construction being completed by 1436.
What many may not realize, however, is that the facade itself was not finally completed until the later 19th century -- a design by Emilio De Fabris who won a competition hosted for this purpose whose challenge was to combine elements of gothic and renaissance design. Prior to this, the original facade designed by the architect of the duomo, Arnolfo di Cambio, was only partially completed to just above the doors -- much like what one sees of the basilica of San Petronio in Bologna today. In the mid 16th century, Cosimo de Medici ordered it to be removed with the intention of furnishing an entirely new design for the facade of the duomo but the competition came to naught and so the facade was left bare, such that if you were to have travelled to Florence anytime prior to the end of the 19th century here is what you would have seen:
And here the facade under construction:
A remarkable design such that were you not aware of its history, you would quite likely have no idea that the facade is in fact much newer than the rest of the exterior of the building.