I'd love to see the paleolithic art in the caves of the Sahara. They date back to the time when the upper African continent was a relatively lush grassy plain, sustaining many animals and plants that are long gone. There are paintings on the walls of these caves that clearly depict psilocybin in a magical-realm context.

I can't imagine that smoking wasn't discovered back in prehistory... humans were much closer to applied botany AND fire.