A mythical network. This network is considered as the greatest Lyons network (excluding sewers). Most of the existing maps were untrue or incomplete, probably intentionally to maintain the legend of mystery. Realistically, the size of the network is small, it develops within 2km. By cons, it is full of small surprises and intertwined levels that make it a very funny underground.

The most likely hypothesis of the origin of fish bones, given the structure of the network, is a military use, or at minimum, shelter and storage.

They were excavated during the construction of the royal citadel Saint Sebastian, symbol of royal authority against Protestants during the reign of Charles IX in 1564. The citadel was destroyed 20 years after the reign of Henry III. It will write up an order for its destruction, to avoid ridicule.