Co-Cathedral of Sant'Antimo (c. 1377), built by the Augustinians and originally dedicated to St. Michael. It is in Pisane-Gothic style, a memoir of the rule of Pisa over Piombino. The interior, with two naves (one added in 1933), houses precious works by Andrea Guardi, including a Baptismal Font. The counter-façade has Renaissance sepulchres of the Appiani family. Also by Guardi is the cloister (1470).
The Rivellino (Walls Tower-Gate), the most ancient monument in the city (1212).
The Chiesa della Misericordia (early 13th century). It houses a precious 15th century crucifix.
The Cassero Pisano(Castle). It is formed by two distinct building, the Fortress, built under Cosimo I de' Medici (1552-53), and the Cassero (late 15th century), the latter used as military jail until 1959.
The Palazzo Comunale (Town Hall), mostly a modern reconstruction of the ancient Palazzo degli Anziani (1435). In the Musters Hall, with portraits of the Princes of Piombino.
Chapel of St. Anne, a noteworthy Renaissance work by Guardi. Annexed is the Torre Civica (Town Tower, 16th century).
The Cisterna di Cittadella (Citadel's Cistern), also by Guardi. On the sides are the portraits of Jacopo III Appiani and his son and wife, later disfigured by order of Cesare Borgia.
Casa delle Bifore (House of the Mullioned Windows, 1280s).
The Natural Province Reserve Padule Orti Bottagone, created in 1998, next to the locality of Torre del Sale.
