You won't miss it!
La Rochelle is full of those! Arcades in city center. Even l'Hôtel de ville has it!
In several shopping streets (including Rue des Merciers, rue Fleuriau), you will find many building with arches on basement. They were built according to the then style but also to protect shops, warehouses from bad weather (rains, storms...). At the basement, rooms are deep.
The arches, as those old and huge buildings, are, most of time, made of stone (!).
See T-logues to have more pictures of arches Everything in the city reminds you of its port and trade activities: the warehouses, the architecture to protect the shops, the boats.