Boulogne-sur-Mer is the smallest of the three main channel ports. The ville basse is pretty unprepossessing but rising above the lower town is a diminutive, cobbled medieval quarter, the ville haute, contained within the old town walls and dominated by a grand, domed basilica. The main tourist street in the ville haute is rue de Lille, where you’ll find the Hôtel de Ville, whose twelfth-century belfry is the most ancient monument in the Old Town (only accessible via guided tour arranged with the tourist office).
The most impressive sight in the ville haute is the medieval walls themselves, set out with rose beds, gravel paths and benches, and providing panoramic views of the city below; it takes about 45 minutes to walk around them. Within the walls, the domed Basilique Notre-Dame is an odd building – raised in the nineteenth century by the town’s priest without any architectural knowledge or advice – yet it seems to work. The vast medieval crypt contains frescoed remains of the Romanesque building and various sacred objects.