The only architectural evidence on the looming hillock known as Poggio Bonizio, the Fonte delle Fate or Fonte di Vallepiatta is for dimensions the largest public fountain in travertine of the entire territory of Siena, as well as an extraordinary example of medieval hydraulic archaeology. Erected around the first years of the 13th century, probably by the unknown "Magister lapidum" Balugano da Crema, it was interred in 1484 to make room for the construction site of the Medici Fortress ordered by Lorenzo the Magnificent. Following excavation work, in 1803 it was brought to light and later restored. It is formed by a portico with six double round arches supported by pilasters. A canalization system collects the waters from the hill and conveys it to basins situated inside. Sited in an archaeological-environmental park, the fountain today is on the itineraries of villages and castles of the area.