The Palazzo Orsini is a gem of Reinassence architecture. The construction phases of the palace in Bomarzo are linked with the vicissitudes of the underlying Sacro Basco, the park wanted by Pier Francesco “Vicino” Orsini. His father, Giovanni Corrado Orsini, married Clarice Orsini, Cardinal Franciotto’s daughter, on 29 April 1520. On 29 December 1519, Siena architect and painter Baldassarre Peruzzi designed the first wing of the palace, placed near the church. The project included a courtyard, a loggia, and a stairway. To avoid the narrow passages of the medieval village, Peruzzi realized a new access road. A vast area beneath the Palazzo and borgo was purchased in order to realize a terraced garden linked with the new road system.
When Giovanni Corrado Orsini died on 21 September 1535, his son Pier Francesco, alias Vicino, concluded the new wing by Peruzzi. The basement was intended for the kitchen and services, the first floor and the mezzanine for residential use.

In 1645, Bomarzo and the Palazzo Orsini were sold to Duke Ippolito Lante della Rovere, who realized the great hall on the first floor where Lorenzo Berrettini depicted the allegory of War and Peace visible in the vault of the room (1660-1661). The stone doors of the first level date back from the 17th century, while the ones realized by Peruzzi are all located on the ground floor. The Borghese family obtained the building in 1836 and commissioned the room overlooking the castles of Mugnano, Chia, and Attigliano. Only after WWII the greatest part of the Palazzo Orsini became a property of the Municipality, which now occupies the apartment of the Galleria with Giulia Farnese’s and Vicino Orsini’s inscriptions.