Standing on a marked, rocky promontory, Ussel castle overlooks the south side of the residential area of Châtillon.
Built by Ebalo II of Challant in the mid 14th century (the date is confirmed by dendrochronological analyses), the castle marks a change in Valdostan fortress architecture. Indeed, it is the first single body castle in Val d’Aosta, which was the last evolutionary phase of medieval castles, and marked the passage between the contemporary castle in Fénis and the rigid forms in Verrès. Having passed on numerous occasions from the Challants to the Savoys and vice versa, the castle then became a prison, until it was abandoned completely. Having bought the castle from the Passerin d’Entrèves family, heirs to the Challants, in 1983 Baron Marcel Bich donated it to the regional authority, which restored it and earmarked it as an exhibition centre.

With a large, rectangular layout, the castle is an example of good masonry that culminates in blind arcades, not present on the north side, and beautiful mullioned windows each different from the next, with floral and geometric decorations. The corners on the south side (facing the mountain) have two round towers, which were originally connected via a walkway, protected by battlements. The south side also has an entrance with an overhead machicolation. The north side, which faces Châtillon, has two four-sided towers, with a slightly projecting watchtower in between, a symbolic element of feudal power. The monumental fireplaces remain, with large shelves placed on the same ascending line, exploiting a single flue, and traces of the stairs and floor divisions.
Before restoration work began, the manor was mostly in ruins; however a precise archaeological assessment enabled identification and reintegration of the missing parts. A picturesque walkway was added along the battlement, where visitors can admire the Châtillon plain and its historic buildings.