Most of us spend one-third of our lives in a state of which we understand remarkably little—some people sleep for only a few minutes a night, and function perfectly well, while others declare that eight hours isn't enough. NOVA explores traditional notions about how much sleep we need; looks at effects of the sleeping pill, and, perhaps the most baffling of all aspects of sleep—dreaming.

Just why did Cro-Magnon man living in France's Dordogne Valley some 15,000 years ago take time out from the desperate business of survival to paint pictures in inaccessible corners of his cave dwellings? NOVA joins French and American archeologists as they piece together the lifestyle of these hunters of the last great Ice Age, and try to interpret the meaning of their cave art.