In the very heart of Siena, you can see this beautiful Gothic-style loggia dating back to the 14th century. This marble chapel was built in order to commemorate the end of the 1348 plague, which hit the city. Note the exquisite sculptures adorning the columns.
Wikipedia (Italian) http://it.wikipedia.org/wiki/Cappella_di_Piazza
Address 3 Via di Salicotto, Siena 53100, Italy
Coordinates 43°19'5.927" N 11°19'55.718" E