Fish bones (also abbreviated ADP) are part of a network of much larger gallery, called Fantasques, due to the name of a road, above the galleries. As its name suggests, the network looks vaguely to a structure of a wheat. In fact, it is a network of parallels arranged around two dorsals (or main roads) with an orthonormal structure, much like certain Nazca archaeological symbols, or even a TV antenna, but definitively not like fish bones.
The main feature of these undergrounds is their purpose was not to drain water, unlike the other two parts of the network (The Colinettes and large galleries). Most galleries are straight, flat, millstone, with dry soil, with the notable exception of the main corridors, steep slope with many stairs.

Forget the ultra-wide angle, choose the fish-eye!

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.

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.

Although there 5m ³ discovered human bones in 1959 during renovation of underground tunnels, it is clear that these underground were not intended to be catacombs, discovered the ossuary is merely an anecdotal reuse of the network.

According to various persistent rumors, the galeries network could be open to the public in the near future, and maybe offering the preservation it deserves.

Meanwhile, various underground openings are bringing the presence of taggers. The most paradoxical is that these openings are often carried out by lovers of heritage assets and they open to vandals every time.