Pisa Duomo
The centerpiece of Pisa is the Duomo, with the accompanying Tower of Pisa, essentially a failed attempt at a campanile.  The marbled architecture is typical of this corner of Italy, with arches and columns engulfing the structure.  Construction started in 1063 and was designed by the architect Buscheto.  The interior is beautiful, and there are some close-ups of the details of the ceiling decoration in the last several pictures.