In 1940 Andrée "Dedée" de Jongh, a young woman from Brussels, created an underground net to help allied pilots to escape from Nazi territories during WW2. The British secret services named it Comet, for their fleeting appearences.
Through this net, which crossed Belgium, France and Spain, the soldiers could arrive to Gibraltar were they could be sent back to Britain. About 878 soldiers were able to escape from the Nazis thanks to the Comète
Nowadays there is a conmmemorative hike to walk the paths used by the people of Comète.