Passage berrichon (Berry passage ©)

This is a narrow passage in a wall seperating the nef (nave) from the bras de transept (transeptarm).
These passages are quite common in the Berry region around Bourges, hence the name.
When these passages are used, the nave usually has a rectangular shape without bas côtés (aisles).
The picture (Notre-Dame-de-l'Assomption - Champlecy) clearly shows the two passages left and right, against the side wall of the nave.

Notre-Dame-de-l'Assomption - Champlecy