You will sail past the Cordouan lighthouse. Lying 7 km from the coast, it marks the entrance to the Gironde estuary, formed from the confluence of the Garonne and the Dordogne rivers, where the tumultuous waters combine with the Atlantic Ocean. Built by the architect Louis de Foix in honour of the kings Henri III and Henri IV, “the lighthouse of kings” was opened in 1611. Raised and restored at the end of the 18th century, Cordouan now stands 68 metres tall. Listed as an historic monument in 1862, this masterpiece of marine architecture is the oldest French lighthouse still in activity. In 1823, it was fitted with the first Fresnel lens, named after its inventor, while over the years its lighting system was electrified then computerised.