Many stairs in the castle of bull Carantec.

The stairs cross of the peak battery. The corridor down the room leads to the research center, while the two others leads to the main ramparts.

The stairs to the bunker beneath the Gare Saint-Lazare.

The last numbered floor stairs.

This stairs is a gift of god. You can access the small belt, a train railway and a technical galery from it.

The Border Cathedral is a labyrinth of stairs and curtains.

Surprisingly, the staircase is the center of the tower. Usually, the stairs are located at the ends or in small adjacent towers.

At stage 34, the orientation of stairs to change.

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.

A Jacob stairs, hidden between two walls. Very slicing!