Beneath the village of Naours in the Somme region of Picardy, France, an underground network stretching over 2,000 meters was discovered in December 1887 by Abbé Ernest Danicourt, a local priest. This vast system includes 28 galleries and nearly 300 rooms, all carved by hand into Picardy limestone. The tunnels average a depth of 33 meters and had remained hidden for centuries before Danicourt's exploration brought them back into the public eye. The underground complex was originally built as a refuge during the Hundred Years' War, a long conflict between England and France that lasted from 1337 to 1453. These tunnels provided shelter during times of war and continued to be used as a safe haven until the 17th century. Later, during the reign of Louis XVI in the late 18th century, the galleries were used by salt smugglers, known as "contrabandiers," who sought to avoid heavy taxes on salt, a vital commodity at the time. One of the most remarkable features of this site is its stable underground climate, which maintains a temperature between 9 and 9.5 degrees Celsius year-round. This consistent environment has helped preserve the structure over centuries, allowing historians and archaeologists to study it in relatively good condition. The design of the tunnels and rooms suggests they were built for communal use, possibly sheltering as many as 3,000 people at a time. The rediscovery of this network offers a glimpse into the resourcefulness of the people of Picardy, who created a vast underground refuge in response to both war and economic pressures. It also highlights the possibility that similar hidden structures may exist beneath other parts of France and beyond, waiting to be uncovered. This site continues to provide valuable insights into the region’s history, revealing layers of human experience that are often overlooked in the landscapes we know today.