Pienza's duomo was built on the site of the Romanesque Chiesa di Santa Maria, of which little remains. The Renaissance church with its handsome travertine facade was commissioned by Pius II, who was so proud of the building that he issued a papal bull in 1462 forbidding any changes to it. The interior is a strange mix of Gothic and Renaissance styles and contains a superb marble tabernacle by Rossellino housing a relic of St Andrew the Apostle, Pienza's patron saint.
There's a small museum in the subterranean baptistry (open 10am to 1pm and 2pm to 6pm mid-March to November, to 5pm Saturday and Sunday December to mid-March, adult/student €2/1).
At the time of research there was talk of introducing an entrance fee to the duomo.