Underground Clermont-Ferrand are dug in the tuff. The tuff is consolidated volcanic ash, easy to dig. Sometimes you may discover metamorphic rock inside the tuff. This is this kind of rock you can see on the left of the photo. Useless and too heavy, it was left in the underground.

The underground lake in the salt mine is over 100 meters long and 40 meters wide. Across the bridge by boat. The scope of the vault is impressive!

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.

One of the underground cathedrals of city's Defense, so called because the vacuum is very large. Before the attacks of September 11, 2001, the underground were opened in the Heritage Days. Since then, all visits are canceled

This underground labyrinth is located approximately 8 meters underground, which makes it ideal properties for the storage of wine.

Most of the inhabitants of Lyon know that subsoil of the Croix Rousse and Fourvière is traversed by numerous galleries. Before the various prohibitions (and even after) to walk the subsoil of Lyon in the late 1980s, students were fond of underground walks. Moreover, there were few entries directly into schoolyards (now closed).

Curiosity, while the soil underground is gross, it is possible to call an elevator to the surface in music! Of course, this stage is not on a secret control panel, it is not possible to go down this way (unless you have a key, perhaps).

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.

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.