But Wait! There's More! Siena Duomo Museum and Baptistry

In the 14th century, the Sienese planned to expand the duomo, making its current nave into the transept, thus creating what would have been (still) by far the largest church in Christendom. But they didn't. (Something about a plague). Anyhow, where the new entrance would have been is (roughly) now the cathedral museum, which contains the treasury, relics, and items removed for preservation.

The original humongous 13th century stained glass window from the east side

Statues, now somewhat weathered, of assorted saints, apostles,demi-gods, et aliud

And another quick and clandestine shot, of probably the most famous painting in 
Siena, Duccio's 1311 Maesta; there are many Maestas in the Christian art world; 
this is the Maesta

Us on the roof of the duomo museum

Looking back to the Piazza del Campo and Palazzo Pubblico

And at the duomo and its great campanile; note that the campanile has an 
increasing number of bays on each floor, ingeniously lightening the load on up...

Meanwhile, back in the museo, an interesting coat of arms 
(nyuk, nyuk,nyuk)

A particularly cheerful display in the reliquary

In the Baptistry, the font by della Quercia

With bronzes by Ghiberti (who bested Brunelleschi for the contract to do the 
doors of the Florence duomo bapistry)

And Donatello