The vaulted cellars of the castle house a section devoted to ancient navigation, centred on two exceptionally well-preserved Gallo-Roman boats. One is an open boat, 10 m long, and the other a barge, which was originally about 20 m in length. Both are typical examples of the Celtic boat building tradition. The open boat, dating from the 4th century A.D. is the sole example so far found of an intermediate stage in boat building between the dug-out, made of a single piece of wood, and boats built of planks joined together. Discovered in Yverdon in 1984 (the open boat) and in 1971 (the barge), both have undergone lengthy and painstaking conservation, which has made it possible to put them on show to the public.