I visited Altamira in the late 60's and for the price of the equivalent of $3US hired an official guide for a day who took me through all the locations open to tourists which were stunning beyond ones imagination and a very spiritual experience.
We then proceeded to go deeper into the complex with our own flashlights and crawled through fissures and saw petroglyphs and finger drawings in the mud floor.
I have seem many cave drawings in South Africa and France but the Hall of Paintings is only second to Lascaux,