Philadelphia, PA - Sunset Beach on Delaware Bay in Cape May, New Jersey, is where you can see the sunken wreck of the World War One concrete ship, Atlantus. She lies there, half-submerged, a few hundred feet offshore.
The Wreck of The SS Atlantus
The weather-worn impact is all that remains of an experimental World War I concrete freighter. She was towed there in 1926 to be intentionally sunk as a breakwater and protection for the entrance to the then-new Cape May Canal. During a sudden storm on Delaware Bay, she broke free of the towboats and was washed into the shallow water a mile or more west of her intended resting place near the Canal.
As it happens, this artificial barrier is the happy accident that makes Cape May Diamonds available to you. See: Sunset Beach's Cape May Diamonds