A team of speleologists (scientists and sportsmen) went on an exploration to find an underground river in the “Gouffre de Romy” more than 600 metres underground located in the mythical Pierre Saint Martin mountain range. During this 15 to 20 hour expedition at the heart of a hostile and magnificent environment, the grotto slowly revealed its secrets: rivers, bottomless wells, huge galleries, narrow passageways. Despite the difficulties to progress in such a hostile place, our explorers managed to complete their expedition and note down geological, hydrological and topographical measures that were observed.