Surprising but true.
All the scenes of the Germans gazing out longingly to sea towards England as Hitler prepares the invasion following the fall of France, were filmed in Guipuzcoa. When a German descends in a jeep towards what is supposed to be the area around Calais, he passes the castle of San Telmo, situated just above Hondarribia.
In another scene we see a German machine gun post looking down on a small harbour. This is also Hondarribia, although the port has since been greatly extended.
Next to the port we can see the Bay of Txingudi, and beyond, Hondarribia. At the same place we will see a smoking German plane returning from the Battle of Britain.