The hole in the ground leads the men into a giant opening, with the true size of the cave revealed in the video clip.
“How many storeys is that?” the cameraman is heard asking, before his friend answers: “Lots.”
What the video shows later is mind-boggling, as the group is seen standing next to a fenced-off section at the end of the cave, which turned out to be an underground military complex from the time of World War II.
The underground military complex is called the Fortress of Mimoyecques and it was used by the German Army during the war.
“The networks of tunnels were linked to shafts where 25 V-3 guns would have been installed. The weapons – which were all targeted on London – were able to fire ten dart-like explosive projectiles a minute,” YouTuber IKS Exploration explained under the video.
These weapons were allegedly so dangerous that British Prime Minister Winston Churchill later said they would have delivered the “most devastating attack of all” during the conflict.
While the missiles are no longer in the cave, the discovery by IKS Exploration amazed viewers.