Check and research "Chauvet Cave" and especially "Cosquer Cave."
"Cosquer Cave" has excellent proof, that not even JWs are able to refute. The only cave entrance is 41 metres below sea surface. So the people painting must have entered, as the sea level was much lower than today. This is a proof, that they could enter only during the ice ages much more than 6000 years ago when the sea level was more than 100 metres lower than today.