It is no doubt the whole Valentino's park's most famous building. Its origins date from the early 16th Century. Emanuele Filiberto of Savoy acquired it in 1564. Later Carlo Emanuele I (the Iron Head's son) bequeathed it to Marie Christine of France (the Madama Reale) who used it as her favourite residence and lived there at length with her court.

The Castle was completely refurbished from 1621 to 1669, first by Carlo di Castellamonte and later by his son Amedeo. The building presents two different façades: the main one towards Turin has the same architectural features as French 17th castles and contains elements of the Italian building baroque style; the other facing the river Po is brickwork. The halls, particularly the Central Hall and the Hunting Room on the first floor (accessed by two stairways) preserve traces of the old 17th Century splendor, with rich stuccoes and allegorical memorial frescoes. The pavement of the large courtyard is chiaroscuro stonework and contains its original design motifs.

Battles were fought around the Castle, agreements and armistices stipulated and alliances signed. Its vaults record the most salient dates of Piedmont's history, as those at Palazzo Madama. Today it is the seat of Turin Polytechnic's Faculty of Architecture.