Located on the Sant'Angelo hill and surrounded by the Ausoni mountains, Sonnino preserves its medieval urban characteristics: the tall four-storey tower, part of the ancient castle, dominates an intertwining of alleys that, starting from the access doors, intersect almost as if in a labyrinth. The city, in fact, was once surrounded by walls interrupted by 13 semi-cylindrical towers, with observation windows, loopholes and walkways for the round and, the 5 access doors were opened in the morning and closed at sunset.
Among the religious buildings we find the church of S. Angelo that dates back to the year 1210, with many references to the Gothic-Burgundian of the Abbey of Fossanova.
The "Collegiate Church" of St. John, in the middle of the historic center, was built around the year 1200, at the behest of fellow citizen Pomponio de Magistris, Bishop of Terracina. It was restored and reconsecrated in 1604 and preserves a fine altar of Romanesque style with a sculptural work attributed to Bernini, and in any case of safe Berninian school.
Then we find the church of San Pietro and that of San Marco, patron saint of Sonnino. Over time it has come to decay, reduced in precarious conditions it was used as a timber deposit. Finally restored it was used as a "Municipal Auditorium", for conferences, concerts. It is also used as a council chamber.
Not to be missed is definitely the Terre di confine Museum whose objective is to revisit the contents of tradition and focus on those moments, those aspects and those characters who participate in the construction of the local cultural heritage.