An Italian speleology expedition penetrates the heart of the Mercadito forest (Chiapas, Mexico) in an attempt to reach two mysterious "sotanos" (open air wells), called "tiger eyes", about which there are many legends and scientific hypotheses. Some people think they were important observatories which permitted the Maya to extend their sophisticated astronomic knowledge. After a week's march in the jungle, the group reaches the entrance to the grotto and discovers interesting signs of the Maya's presence.