Between 1659 and 1815 Philippeville was an ultra-fortified enclave of France, completely encircled within the Holy Roman (and later Habsburg) Empire. At the eastern end of the main square, the tourist office organises fascinating 90-minute guided walks through sections of the fort’s subterranean passageways, the souterrains, of which more than 10km remains.

The walks start with a useful introductory video and culminate at little Chapelle des Remparts, a unique chapel fashioned from the citadel's former gunpowder store.