They arrived at the underground lake topped by the air bell seen by Cosquer in 1985. Their guide line being too short, the Van Espen brothers were forced to turn back in order to exit safely by following their guide line towards the entrance of the gallery without being able to emerge in the bell. At this stage, the non-submerged part of the cave had still not been explored. In June 1991, Marc Van Espen was back in Cassis and on June 24 he dove again with Henri Cosquer, both of them determined to finally go to the end of this cave. On this occasion, Marc Van Espen achieved the installation of the last section of the guide line essential to the safety for progression into the immersed part of the cave. Their incursion into the cave only lasted about thirty minutes and only allowed them to briefly explore the first room to which the sump gives direct access. A few days later, on July 9, 1991, Cosquer decided to go back to explore the cave to estimate its extent in the company of friends and instructors of his diving club: Cendrine Cosquer (his niece), Yann Gogan and Pascale Oriol. It was during this dive that a more detailed exploration of the unflooded part of the cave was carried out. Yann Gogan then saw the outline of a hand on a wall, while Pascale Oriol put forward the hypothesis of a cave painting. This discovery, as disconcerting as it was unexpected, prompted the "team of four" to return and actively search for other traces. Several dives in July and August 1991 enabled them to discover the cave paintings and to make films and photos with the help of Thierry Pelissier and Gilles Sourice (Fanny Broadcast – Les films du soleil). On September 1, 1991, there was a triple fatal accident in the cave. Three divers from Grenoble did not find the exit of the access gallery (175 m). Henri and Yann participated in the recovery of the bodies of the three victims in the gallery. Two days later, on 3 September 1991, Henri declared the cave to the Maritime Affairs Department in Marseille. The file was transmitted to the Direction des recherches archéologiques sous-marines (DRASM) and then to the Service régional de l'archéologie (Regional Archaeological Service) under the Ministry of Culture. An expertise took place from 18 to 20 September