"Mullberry Harbour" a Arromanches-les-Bains Travel Page by DrexlUK

Constructed in the UK and then (slowly) towed across the channel to help with the unloading of Allied troops and equipment during Operation Overlord.

The remains are visible across the beach at Arromanches with some of the parts of the harbour close enough to be walked to at low tide. Even in their decaying state, the parts of the harbour are still quite impressive. See photo for idea of size/scale.