One of the most eyes openning book I ever encountered is “The doors of perception” of Aldous Huxley.
The main take away is that intelligence and knoewledge are not inside the individual, or a property of the individual, but all depend on whether the curtains between the individual and the outside world has been lifted or not.
If the doors of perceptions are not opened, people could only enjoy an infantile life made of second hand experiences and knoweledge reported by the people lucky enough to have the curtains lifted for them.
In Da Vinci notes, he stressed the need to continuously train the eyes and our other senses in order to be fully awake to the world. He prefer to think with images, instead of abstract concepts. For Da Vinci anatomy is the royal door to deep knowledge.
Aldous Huxley used the drug mescaline to first experience the lifting of the doors of perception. Though he enjoyed that a lot, he cautionned about taking the easy road to knowledge trough drugs.
Da Vinci was wild on sex and used drugs like syrian rue and some attention enhancing herbs which he called “miracle nutrients”
Prolonged direct contact and observation of nature, ideally alone, while facing some life challenges often lead to the opening of the doors of perception, too.
Once a door is open, more doors would start opening. Life time experience.