Recorded at the end of the 13th century, the hermitage stands on the margins of what was called, in the medieval period, the lake of Verano. The lake was situated south of Monteriggioni but is no longer in existence. When it became part of the congregation of the Hermit Brothers of St. Augustine in 1243, S. Leonardo it was aggregated to the nearby hermitage of Lecceto a few years later where it remained until 1516. At the start of the fourteenth century, the Blessed Agostino Novello, an important religious figure who had taken up residence during the last years of his life, died here.
A noteworthy element of the architectural complex is the beautiful church with a single nave built entirely in stone, excellently conserving the simplicity of its medieval lines. Inside, the small square apse is decorated by a cycle of 14th century frescos by the Siena born painter Lippo Vanni. To the side of the church, as well as the remains of a defensive wall with turrets, there are cloisters and a part of the monks' dwellings, amongst which should be highlighted the refectory frescoed by Giovanni di Paolo in the 15th century.
Not far from the hermitage of S. Leonardo stands the so-called Pyramid, an obelisk to the memory of the eighteenth century draining of the area below, which is still known today as the Pian del Lago (the Lake Plain). The Pyramid also signals the start of the Grand Duke's canal, a tunnel of around two kilometres long which served to permit the running off of the waters and which is perfectly preserved and still usable today.