Mulberry harbours” in the Allied invasion of Europe in WWII. After the invasion the Mulberry harbors were largely demolished, though a few pieces remain above water off “Gold Beach” in Normandy.
Now scientists from the United Kingdom, using sophisticated sonar systems, have located the remains of the “Port Winston” Mulberry harbor, some just 15 feet underwater.
In my travels around Europe (including Eastern Europe), one of the most surprising things to me was just how little directly visible evidence of WWII remains. After my readings of history, and given how recent WWII was, I fully expected to see direct evidence of it all over the place. Here's a great example of what I mean – these Mulberry harbours were enormous constructs of concrete and steel, and yet they were completely lost for 69 years! When I visited Normandy roughly 20 years ago, I was shocked to discover that very little of the massive Nazi defensive works remain, and those only because they were preserved as a monument. Even in the former Soviet Union it's hard to find remnants, though there are more there than in the West. For example, on the southwest tip of the island of Saremaa (in the Baltic Sea), there is a largely untouched concrete defensive works, quite large, still remaining – and there are some efforts to preserve what's left. Most of the iron and steel components of this works have been scavenged, but the concrete bunkers remain.