The Natural History Museum of the Accademia dei Fisiocritici of Siena, housed in the former Camaldolese monastery of Santa Mustiola dating back to the 12th century, is one of the oldest and most important scientific museums in Tuscany.

The Academy of "Fisiocritici" founded in 1691 by Pirro Maria Gabbrielli, professor of Medicine and Botany at the Sienese University, brought together many scholars who met periodically to discuss scientific issues and research the truth of natural phenomena through experimental practice . Indeed, the term "Fisiocritici" which means "judges of nature" or "those who study nature" derives from this.

Considered one of the most famous cultural societies in Europe, among its members it had scientists such as Carlo Linneo, Joseph-Louis Lagrange, Alessandro Volta, Louis Pasteur. The exhibition, whose original nucleus dates back to the mid-18th century, collects naturalist and historical finds, period instruments and curiosities and is organized into four sections.

Particularly significant are the "Paolo Mascagni" collection, with anatomical preparations made with the technique of injecting metallic mercury into the lymphatic vessels, but also the "Francesco Valenti-Serini" collection which includes a large collection of terracotta models of mushrooms and a lichen herbarium. In addition, the “Francesco Spirito” collection, with anatomical preparations treated with the petrification process, is noteworthy.