We are in the unhosptable region of Iceland, the approach march to reach the frozen cap of Vatnajokull, an active volcano and an adventure in itself. The odyssey of the speleologists, equipped with scientific material worthy of real sepleonauts, occurs among crevasses route among lava and ice, in search of an underground river with warm water that produces toxic steam. The water comes into contact with the fire repeatedly along the river where the cavities are similar to alveoli and intermittent geysers: all together a fascinating journey.