A study was carried out over a period of more than two years of the seasonal variation shown by the different variables that determine the microclimatic and chromatic characteristics of the Altamira Cave, Spain, under natural conditions, i.e., in the absence of visitors to the cave. The Altamira Cave contains 16,000-year-old prehistoric paintings and as such is a priceless legacy from the distant past. Temperatures of the air, floors and roofs, air humidity, and CO₂ concentrations of the different chambers of the cave were measured. Flow rate and chemical composition of the waters flowing into the paintings chamber were also analyzed. A chromatic characterization of the paintings, determining the psychrometric coordinates of the color, lightness, chroma and hue, was made. This study has not only enabled presentation of the state of conservation of the famous polychrome roof of the Paintings Chamber, but has also supplied a reference point for later studies. Future experiments could be made with various controlled regimes of visitors to the cave in order to establish suitable criteria for the best possible preservation of cave paintings. -- AATA