In the 16th century, the Bourg citadel, the stronghold of Bordeaux, was elevated to the rank of impregnable citadel thanks to the work of the Duke of Épernon, whose vaulted passage remains a vestige that you can discover during guided tours. You'll also visit the basement, where the former stone quarries were used to build impressive 70-meter-long reinforced concrete oil tanks, used during World War II. The Bourg Citadel Museum is located near the castle, which features 18th-century neoclassical architecture. You'll be amazed by its collection of horse-drawn carriages, which you'll learn about during guided tours.