The cave of Saint-Marcel is known for its extensive network (64 km of galleries)and its history of human occupation (Middle Palaeolithic and Neolithic) in theentrance area. Close observation of the main network reveals areas with high concentrationsof broken speleothems, which are usually attributed to the first touristvisits of the nineteenth century. However, archaeo-geomorphological mapping of thebroken speleothems, many of which are lying on the floor and sealed by stalagmiteregrowth or crust, indicates intentional organisation of the underground space intospeleothem supply zones and zones in which the speleothems were used to buildstructures. Age estimates of the stalagmite seals on these human-made structuressuggest that the structures were a result of human activity that occurred between theend of the Upper Palaeolithic and the European Mesolithic. These age estimates radicallychange the way we look at the broken speleothems in the cave of Saint-Marceland the structures associated with them. They bring to light the engagement of pasthuman communities with the deep underground environment, at more than 1.5 kmfrom the cave entrance, which can only be accessed by crossing obstacles (pits) that,today, are considered as difficult to be crossed. Our findings and ongoing researchstress the unequivocal archaeological significance of the cave.