La Cité de la Mer turns Cherbourg's old Transatlantic Maritime Station into a full maritime museum. The building alone is part of the appeal: this was where ocean-liner passengers passed through when Cherbourg was a major Atlantic port.
Inside, the big draw is Le Redoutable, the former French nuclear submarine that visitors can walk through. The permanent Titanic section links Cherbourg to the liner's final voyage and displays artefacts recovered from the wreck field. It is the kind of museum that can easily take half a day if you are interested in ships, engineering, or sea travel.