The Sanctuary of Montenero (Santuario di Montenero) is a religious complex maintained by Vallumbrosan monks. According to legend, in 1345 a shepherd discovered an image of the Virgin Mary and carried it up the "black mountain" (monte nero), which was known as a refuge for brigands. A small chapel was founded in honor of this miraculous image, and expanded over the centuries.

While the church itself is beautiful and Baroque, with a gorgeous nave featuring the last intact carved wooden ceiling in Livorno, the real attraction is in the surrounding rooms and hallways. On the walls hangs Italy's largest collection of ex-votos (votive offerings, short for the Latin ex voto suscepto: "from the vow made") giving thanks to the Madonna for saving her devotees from disaster.

The collection starts in the early 1800s, mostly with paintings, and as the exhibition continues, later offerings include photographs, clothing, reproductions, and heirlooms. Many depict near-death incidents at sea, fires, or war, but the gallery also contains plenty of images of avoided fatalities in daily life, from the common (carriage and car accidents) to the unique (a pot falling from a windowsill onto a person's head). Some are of great artistic value, including paintings by Giovanni Fattori and Renato Natali, though most are amateur works of folk art.

Also included in the complex is the monastery, a portico containing tombs and memorials to illustrious Livornesi (formerly a dormitory for pilgrims), a bell tower with a mechanical clock and sundial, a gallery of the coats of arms of Tuscan municipalities, and grottoes in the hill behind the sanctuary that were used as a hideout for bandits in ancient times and as an air raid shelter during World War II.