The pentagonal tower of San Pio delle Camere

The Castle of San Pio delle Camere, located in San Pio delle Camere, L'Aquila, province of Abruzzo, Italy, is a remarkable example of medieval architectural ingenuity. First mentioned in 1173 as a fief of the Barons of Poppleto, the castle later came under the House of Caracciolo. The castle's unique pentagonal tower, formed by a regular five-sided polygon, is its most striking feature. The plan of the walls, encompassing the tower, is triangular. The smaller towers along the walls are an interesting extension of the castle's structure. Notable changes to the castle's design can be traced back to various times throughout its history, as indicated by the raising of the walls at different points in time.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons