Recently, a type of stromatolite not known to date was discovered in El Soplao Cave (Cantabria). But, since caves have no light, how is it possible for microbes to perform photosynthesis, which is necessary to build the stromatolithic structure? The answer to this and other questions was recently published in the prestigious scientific journal Geology (Rossi et al., 2010*). This finding is the result of research carried out in El Soplao Cave by members of the Spanish Geological and Mining Institute (IGME), the Complutense University of Madrid and Melbourne University (Australia). The research work was conducted as part of an agreement to study the cave signed by the IGME, the Department of Culture, Tourism and Sport of the Regional Government of Cantabria and the company SIEC.