Now Danish authorities are tearing down, or blowing up, the bunkers to protect swimmers and holidaymakers from the crumbling remains, the Frankfurter Rundschau newspaper reported on Thursday.
"The bunkers did not exactly make our beaches more beautiful," said Iver Einvoldsen, mayor of Ringkøbing, which is on the 50-kilometre stretch of coast where the huge concrete defence structures are being torn down.
As the weather has taken its toll, the concrete has started to fall to pieces, exposing sharp and rusted iron reinforcement rods, on which it is feared tourists could injure themselves.
Yet some Danes are upset that the bunkers are being removed from the landscape.
"This is part of our history. One is removing something which could have great meaning for future generations," said Louise Kjaer, a landscape architect. She said the landscape was given edge by the bunkers, and they were relevant in an age where much about World War Two was being forgotten.
The bunkers were part of the Atlantic Wall, an enormous series of defensive structures built to protect the Third Reich from sea-based invasion. It stretched from Norway to Spain. The Danish section was built between 1942 and 1944 - by Danish companies who made huge profits from the business, the Frankfurter Rundschau said.
Post-war attempts to destroy them failed and they were abandoned to the weather - which has now done enough of a demolition job that they can be torn down.
"The old bunkers are reminders of a dark chapter in Denmark's history that we cannot be allowed to forget," said Environment Minister Pia Ohlsen Dyhr. "But we have to accept that some of the bunkers have become a risk to tourists and swimmers. Now we are removing the most dangerous, to the delight of all of those who enjoy our beautiful west coast environment."
The remains will be used in road-building projects. Work started this week to demolish around a fifth of the 600 or so bunkers along the coast.