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Basilica of Notre-Dame-de-l'Immaculée-Conception, Boulogne-sur-Mer: 101 meters. The Notre-Dame basilica was built between 1827 and 1866 by the abbot Haffreingue, on the ruins of the old cathedral, destroyed shortly after the Revolution. This colossal ensemble is inspired by several great monuments such as St. Paul of London, St. Peter of Rome or the Pantheon. Not to be missed inside, the high altar of the Torlonia princes, masterpiece of the Italian mosaic of the nineteenth century. © Shutterstock