This museum is a highlight that one would not expect to find attached to a fine, but small, country church, such as San Pietro a Cascia is.
The museum is explained by the purpose to gather in one place, to keep them safely, works of art once scattered in different churches in the Reggello countryside. In this way, works of art (not only paintings, but also plenty of liturgical vestments and goldsmith works) that otherwise would have been visible with great difficulty, and in different places, constitute a "critical mass" such as to make it possible to open the museum with a relatively extended visiting hours over the week.
The museum is therefore configured as a real museum of the territory. Even the most precious piece of the collection, the so-called "Triptych of San Giovenale", takes its name from a church in the area, San Giovenale in fact, where it was formerly guarded.
This work is considered the first one by Masaccio, being dated 1422 (Masaccio was born in 1401, in nearby San Giovanni Valdarno). Masaccio is the first of the Tuscan painters fully belonging to the Renaissance era, in his short life (he died in 1428 or 1429) he was a real renovator of his art, which reached its peaks at the Brancacci Chapel into the Chiesa del Carmine, Florence.
The museum layout is also very valuable.
Basically, it's an attraction not to be missed.