Exploring the original cave requires a 30-minute hike to the foot of the limestone cliffs above the Ardèche River and then up a winding path to a simple rock shelter where visitors, rarely admitted, leave their belongings. At the cave’s entrance, journalists donned coveralls similar to those used in a hospital operating room, special rubber shoes, a helmet equipped with a headlamp, and a harness and belt to attach to the ladders and cables that extend into the cave’s depths. The goal is to protect the cave from contamination by anything on the visitors’ clothes or skin.

Then came the descent through a narrow opening in the rocks. As the air became cool, dark and damp, it was like entering another world. The darkness was encompassing; the light from the headlamps did little to illuminate the rock chamber’s depths, and the walls receded in darkness and shadows. The sounds of dripping water and echoing steps were magnified in this vast blackness.

Headlamps bobbed as the visitors followed metal walkways installed to protect the soft cave floor, with its prints of bear paws and the shallow depressions they dug as sleeping areas where they hibernated. The lamps revealed the cave’s extraordinary beauty: Stalactites and stalagmites sparkled as if crushed diamonds had been mixed with the sandy colored rock. The cave seemed alive, even growing, with new finger-length stalactites forming on many rock surfaces like the thinnest, most delicate of icicles. Those glittering surfaces are more recent than those of the flatter rock where humans drew their images, Ms. Badisa said.

On the walls, lions stalked, and a remarkable owl stared down from a branch, its head turned all the way around so that it was regarding us over its wings. Less familiar were the mammoths — a hairy relative of today’s elephants — and the aurochs, large horned wild cows that are also extinct today. The detailed nature of the drawings suggested how closely entwined the human and animal world must have been, allowing for close observation of the horses’ manes, an owl’s feathers and the black markings on the rhinos’ torsos. The bulk of the bodies and the play of shadow and light are reminiscent of Picasso, and it is hardly surprising that he visited other prehistoric caves and was struck by the paintings’ extraordinary life.