Joseph Vallot, geographer, naturalist and mountaineer born in 1854 in Lodève, was a visionary man, full of humor and whose curiosity was insatiable. He had spent some forty years of his life studying the Mont Blanc massif, sacrificing a good part of his fortune to this multifaceted passion. He was notably the first to demonstrate that one could sleep, work and even do science at an altitude of over 4000 meters, at a time when ascents to the summit of Western Europe were still adventurous expeditions. This documentary tribute follows in his footsteps, via the route taken at the time, on foot from Chamonix via the Grands Mulets refuge to the summit of Mont Blanc to the Joseph Vallot observatory nestled at an altitude of 4400m, with a team of guides, journalists and scientists.