In the story the Black Prince avoided Bordeaux and chose Arcachon as an alternative to keep the mission a secret.
Phare du Corduan
In fact the entry to the the Gironde estuary leading to Bordeaux is not easy either the lands either side of the estuary are relatively flat and the lack of landmarks made it difficult to navigate. a series of towers were erected all of different profiles to assist navigation, the entrance to the estuary being dominated by the Phare du Corduan. The first lighthouse on this site was built on the orders of the prince himself.
The current lighthouse is known as the “Versailles of the sea” because of its elaborate interior, which is only fitting as the magnificent city of Bordeaux is known as the “Paris of the south”.