At the northwestern end of bd de la Liberté, this massive, star-shaped fortress was designed by renowned 17th-century French military architect Vauban after France captured Lille in 1667, and completed in 1670. Made of some 60 million bricks, it now serves as the headquarters of the 12-nation, NATO-certified Rapid Reaction Corps – France. The only way to visit is by guided tour.
Outside the 2.2km-long ramparts is central Lille's largest public park, the Parc de la Citadelle, spanning 60 hectares.
Children will love the park's small zoo with 400 animals (10am to 5pm Wednesday to Monday late February to late November; free) and amusement park, Cita-Parc (www.cita-parc.fr).