The English version of an article giving a short description of the prehistoric rock paintings and engravings in Tassili N'Ajjer, Algeria. It explains why the heritage of this unique open-air museum for Neolithic civilization of the Sahara is in danger and what can be done to preserve it. UNESCO has been working with the Algerian government to promote acceptable forms of tourism, while ICCROM is experimenting with the application of silicone to preserve the paintings. French and Spanish language versions are found.