A small, intense military museum built directly above a section of the underground siege galleries that saved Turin from the French in 1706. After a short introductory display you descend a long staircase into the actual seventeenth-century mines: cool, low, dripping tunnels where the Savoyard defenders dug to intercept French sappers.
The guided tour is the only way to visit the tunnels, and it is gripping — equal parts engineering, military history and ghost story. Reserve ahead; English-language tours run on some weekends. Among the best small museums in Turin.