This route runs through the Orba valley, an area full of castles, and five villages that were once the domain of the marquesses of Monferrato: Castelletto d’Orba, Silvano d’Orba, Casaleggio Boiro, Mornese and Montaldeo. It's easy going and mostly winds along small tarmac streets with pretty views. The beautiful paths of the Strada Costiera di Silvano d'Orba take you from Castelletto d'Orba to Silvano d'Orba and on to Casaleggio Boiro. The river Orba begins in the Ligurian Apennines on the southern slopes of Monte Reixa (1183 m), under Monte Beigua. It's the main right-hand tributary of the river Bormida, which pours in turn into the Po.
Start in Castelletto d’Orba, in Piazza G. Marconi, home to the council building, the church of San Lorenzo and ample parking. Come out onto the SP 175 and as soon as you reach the church of the Madonnina, turn left onto Strada Gallaretta. This road will bring you to Silvano d’Orba, which is dominated by the medieval Adorno castle, which has a military aspect, with four huge well-crenellated towers on a square plan. Nearby are the ruins of a keep, all that remains of another castle that was destroyed in 1446, for which the first records are from 1182. It belonged to the marquesses of Bosco and later to the city of Alessandria.
Enter the village on Via XX Settembre and after 500 m turn right onto Contrada Zucca, then left onto Via Pertini until Via San Pancrazio on your right. Here begins the track that leads to the 12th-century shrine of San Pancrazio atop the hill above the town. Carry on along country roads over the ridge on the right-hand watershed of the river Piota to the lower Orba valley, Mornese and Casaleggio Boiro. 11 km on you'll find yourself at a junction. Turn left for Mornese on a small tarmac road, then right on the track to Casaleggio Boiro. In the distance, 1,500 m away, is the village's castle, one of the oldest in Monferrato. This building was the location for certain scenes from the Rai TV production of I promessi sposi (The Betrothed), directed by Sandro Bolchi and broadcast in 1967. It was used as the castle of the Unnamed in the story. Once you reach the village, go left in the direction of the castle then left further on for Località Cascinotto. At the junction afterwards, turn left until you reach the SP 170, where you must turn right for Mornese on the border of the Lemme valley, the highest point on the route at 372 m.
The imposing castle of Mornese sits atop the little hill that defines the village. It was built in 1270 and rebuilt by Genoese troops after they destroyed it in a bloody battle in the 14th century. Go over some ups and downs (mostly downs) to Montaldeo. It's worth stopping here to have a look at the castle, built in the 13th century, which has a monolithic structure over two floors, plus a large round platform, with four crenellated towers. Like every castle, this one has its own ghost, that of the cruel feudal lord Cristoforo Trotti, killed in 1528 along with his family. The cellars of the castle are evocative, with their dungeons, labyrinths, staircases, traps and instruments of torture. Once you're back in Castelletto d’Orba, you can visit the beautiful medieval village with its stone houses and thin streets winding up the hill. In the centre of the village you will find the 13th-century castle, while at the cemetery you'll find the little Romanesque church of Sant'Innocenzo. The village owes most of its notoriety to its many medicinal springs, all mineral, some sulphurous. You'll also find the large Lavagello water park.