The Germans built the Kahl-Bürg after Operation Jubilee, the unsuccessful raid on the shores of Dieppe which saw the loss of hundreds of Allied (largely Canadian) soldiers in 1942. Using prisoners of war, many of whom were Ukrainian women, they dug deep into the impressive chalk cliffs of Le Tréport to create an expansive bunker, or an “underground castle” over a period of two years. It consists of 32 rooms on four floors and has five openings to the sea and the city, including three observation posts and two combat posts.

For 60 years after the Battle of Normandy, the Kahl-Bürg remained abandoned. It was not until the early 2000s that it was restored, becoming one of the best-preserved sites of WWII. The site remains open thanks to the work of dedicated volunteers.