This well, dug under the orders of Pope Cl,ment VII of the Medicis in order to provide water for the town in the event of a siege, is by Antonio da Sangallo the Younger; two spiral staircases, lit by 72 windows and topped by two people (one going up , one going down) in such a way that they never seem to cross, go down to a depth of 62 m to some very pure water.