In this case, is deal of a German coastal artillery position in Denmark. It was a heavily defended section of the 'Atlantic Wall' built by Nazi Germany during the World War II. 

The MarineKüstenBatterie (MKB = Navy Coast Battery) in Lokken, Jammerbucht bay, Northern Denmark, North Sea coast, was built in 1942. It was headquarters of the 509 Battalion of 40 Navy Artillery Regiment. Battery Lokken was armed with four 12,7-cm guns, emplaced late in 1944. Battery included two 7.62-cn Russian guns and two 7.5-cm guns for local defense. It was manned by 4/509 MAA (350 men). There was two searchlights.

They were originally built behind the 1st row of dunes, but over the years the bunkers of the battery slipped down to the beach because of the erosion caused by the wind and the waves.

It's a shame that everything had graffiti painted on all the walls, but well worth being shown this WW2 German defense position.