This museum on the shores of Lago di Nemi was built by Mussolini to house two Roman boats salvaged from the lake in 1932. These dated from Caligula’s time but were tragically destroyed by fire in 1944 – what you see now are scale models. Further exhibits illustrate the area's Roman history and the cult of Diana, which was popular around the area in ancient times.
Note that the museum is best accessed from Genzano, not the town of Nemi.