High above the valley, the ruins of the Del Carretto family castle are the most striking historical remnant in Cengio. The Del Carretto family held this fortress from the 12th century onward, and the site commands views across the Bormida di Millesimo valley and the wooded ridgelines beyond. The Spanish attack of 1648 left much of the medieval structure in ruins, and what remains today is a fragment of walls and towers embedded in the hillside vegetation.
The walk up from the town centre takes about 20–30 minutes on a steep path through the woods. The views from the top are the main reward: on clear days you can see south toward the Ligurian coast and north across the lowlands toward Piedmont.