From the enormous walls of Cennina, at one time competed for by Siena, Arezzo and Florence, follow the route towards Duddova, an ancient property belonging to the Ubertini nobles. To reach the town, cross a small stream and continue descending towards Mulino la Doccia, where they used to produce wheat and chestnut flour.
Continuing down an unpaved road in the open countryside, you will come to a fork where you turn to the left; at the end of the slope you will find the buildings of the 18th-century Mulino di Rimaggio (a former mill). Over a masonry bridge, passing the ravine and then, constantly keeping to the left, you will return to San Martino.
This tour is part of the guide book Il Diario del Viandante, by the municipality of Bucine. On the official website, you can find details about the routes, useful information and maps to download.