The mysterious subterranean facilities in Picardy have been the subject of passionate research for nearly two centuries. Until the last seventies, the problem could only be studied from previous written sources, but now further advances can made thanks to increasing wealth of archaeological data. To be considered in the countryside is a substantial number of underground facilities known a "muches" (hideout), the earliest of them dating back to the second half of the XVIth century and the first half of the XVIIth century, as confirmed by written sources, graffiti and archeological data. They were rationally created, in an original style : long tunnels with branching-off corridors, lined with rooms with varied fittings. They witness both the...