The Tour de la Chaîne is the northern of the two harbour-mouth towers, smaller and slimmer than Saint-Nicolas across the water. The name comes from the great iron chain that was raised between the two towers every evening to close off the port. The tower today houses a small exhibition on the Huguenot exodus of the 17th and 18th centuries — La Rochelle was a Protestant city and the largest French port of departure for the Huguenot refugees who settled in England, the Netherlands, and the new world.
The terrace at the top gives the best framing photo of the harbour entrance, looking back through the gap to the inner port. Climb both towers if you can — the contrast in mass and feel is one of the small pleasures of La Rochelle.