Lezennes, now a suburb of Lille, has extensive disused quarry workings beneath it. Much of Lille was built from this stone, including the Vauban Citadel in the city. During World War II a number of air-raid shelters were built within the former workings to protect the residents from air raids.
Access is largely impossible but a small section is accessible from within the former Town Hall (Mairie). This section is sometimes open by arrangement - for example during the September Heritage Weekend. The full length of the workings is estimated by some as up to 100km. Parts of the network are below the water table and therefore flooded.
When visited in 2005, evidence of the former working quarry was limited - probably due to its re-use in World War II. Much of the floor had been raised and levelled on waste stone but shafts to the surface for stone extraction were still visible. After its working days, the quarry was used in parts for growing mushrooms.