The Grotte Margot has been open for visits since the 1870's but the first ice age art was not discovered until 2005! Archaeologists have found engravings and drawings of horses and rhinoceroses along with hand stencils and other signs. The decorations appear to be from two eras: the Gravettian (23,000-29,000 years ago) and the Magdalenian (9,000-12,000 years ago) and more images are still being found. There is another prehistoric dwelling cave here (Grotte de Rochefort) that you can also tour, but there is no artwork in this cave.
These caves are part of the Canyon de Saulges park, a beautiful nature park about an hour west of Le Mans, and are unusual because there are very few decorated caves in this part of France. There are many prehistoric educational activities for children and you can also take rock climbing lessons here.
Guided tours only, tours are in French. I have not been able to find out if the normal tour shows you any of the decorations, but they do offer special tours that showcase the art, mostly in the summer. Click here for their schedule of special events. Reservations are required for special tours and are recommended during the summer and holidays.
Caves are closed from November 15 to March 15. Canyon is free to access all year.