"In the heart of a silence just interrupted by my air bubbles, darkness gives way to this freediver that goes back and forth from the bottom of this cenote to the surface," says photographer Fabrice Guerin. "This freshwater sinkhole, calm, clear and without current, is ideal for training. A sulfur cloud located about twenty meters below reflects the sun rays which then work a real miracle. Originally the hydrogen sulphide layer is flat, but as we enter it repeatedly, clouds form, giving us an impression of underwater waves."