Who hasn’t walked past the Trou du Glaz or the porche du Guiers Mort? Probably none. But few of them know that these 2 majestic entrances are linked by 3km of shafts and galleries. And that’s exactly what this long-undiscovered tour is all about. After an initial technical section, including the splendid 36-metre shaft, you reach the “geological floor of the Guiers Mort” and its gigantic galleries. A grandiose underground expedition for thrill-seekers and lovers of breathtaking scenery.