Here is a lovely drone video by François Monier of what is left of Mulberry B just offshore near the French village of Arromanches.
One of the reasons that the Germans were skeptical of an Allied invasion of Normandy was the lack of a nearby harbor through which to unload men and supplies. The Allies addressed the problem by building Mulberry harbors, two massive portable harbors which were fabricated in Britain in modules, towed across the Channel and then reassembled off the coast of Normandy shortly after D-Day, in 1944. Mulberry A was assembled off Omaha Beach, while Mulberry B was installed off Gold Beach near the French village of Arromanches. During the eight months that it operated, the Mulberry off Arromanches was used to disembark two and a half million men, a half million vehicles, and four million tons of supplies. To learn more, see our post from June 2016, The Mulberries Battle the Storm — June 19, 1944.