Hidden behind a plain façade on Vicolo delle Scotte, in the old ghetto established by the Medici in 1571. The synagogue inside is an unexpectedly fine neoclassical interior dating from 1786 — a tall single room with a marble Ark, gilded torah scrolls, and women's gallery upstairs.
Open by guided tour only, usually a few times a week through the Jewish Cultural Heritage organisation; check ahead. The Jewish community of Siena, never large, was deported in 1944.