The Visconti Castle with its semicircular tower stands in a dominant position above the medieval burgh of Vogogna. The fortification was ordered by Giovanni Visconti in 1348, when other sections were added to the original nucleus of the Castle, made up of the square Tower and the walls. The Castle was designed as a military fortress for the defence of the whole valley and especially the burgh of Vogogna, which at that time became the capital of the Lower Ossola.

The central body of the castle, delimited by the semicircular tower to the west and the square tower to the east, is protected from the outside by the long boundary walls. Inside it is divided into three floors, originally used as living quarters. Each room has a fireplace for heating, and some still retain stone shelves or traces of masonry. The rooms on the top floor are today used for conferences and exhibitions.

The semicircular tower, almost 20 metres high, is divided inside into five floors. Up to 1914 it was used as a prison; the small cells are still intact, as are the incisions made by the prisoners on the walls. Since the castle was restored some of the cells have been used for temporary or permanent exhibitions.

The square tower is the oldest nucleus of the castle. Today the Multimedia Centre occupies its rooms, which are used for consulting or reproducing multimedia documents.

Above the castle are the remains of the Rocca, an ancient fortress standing on a high rock from which the whole valley floor of the Ossola could be controlled and defended. In 1348 further defensive features were incorporated into the structure; it was reduced to its present state in 1514 by enemies from Domodossola flanked by armed bands from Switzerland.