In the south of the Massif Central (France) lie the limestone plateaus that form the Grands Causses region. Bordered by the deep valleys of the Tarn and Jonte rivers, the Causse Méjan is the highest of them. Its particular relief, called karst, is marked by the mechanical and chemical erosion of the limestone. The water that seeps through the cracks from the surface of the plateau creates an original topography, characterised by surface phenomena and a large network of underground cavities. The "avens", as they are called in this region, are chasms that open up in the ground. Of variable depths and aspects, their access is most of the time difficult, since they present the shape of a vertical shaft on the whole or part of their development. Some of them were explored as early as the Neolithic period because of the resources they contained (water, calcite, clay), and were considered for a time as the entrance to the Underworld in a land where the Catholic religion prevailed at the time. In the 19th century, these abysses and their exploration were brought to light by the interest of a young lawyer with a passion for geography. At the end of the century, when photography was invented, Edouard-Alfred Martel and his collaborators carried out numerous explorations in this territory of the Causses Majeurs, thus contributing to its development as a tourist attraction and to the foundation of modern speleology. On the outskirts of these caves and abysses, the time of human history and the formation of the soil are intertwined. Crossed by water and by those who still explore them, these lightless spaces preserve the possibility of a world that resists, like the deep seabed, to human knowledge. These images taken with a large-format camera mark the beginning of a research project in which, oscillating between the surface of the medium and the thresholds of the earth's surface, we are confronted with the moment when something of the world as we represent it tips over.