The link above sends you to a PDF of the book called "Ultralearning". I chose this book as the guide to improving one's mind because of my definition of what intelligence is. To me, to be intelligent means to be able to learn new concepts and become master of them quickly.
It's not inconceivable that we can know everything a genius knows, given enough time. What sets geniuses apart from the average man is that the genius can learn much faster. What the average man will learn in college, a genius might already have learned in childhood.
Ultralearning is a guide on how to learn a subject quickly and make it stick. At the end of the day, we want to be intelligent so that we may be more able to complete our goal. In this sense, a book like ultralearning is exactly what one would need.
Wisdom and philosophy is likely what ancient greece is most well known far. It can be said that they were the culture that would set the foundations of our modern world. In some schools of greek philosophy, there is the concept of essence. Essence is what makes a thing that thing. For example, what makes a knife a knife is the combination of the blade and the handle, with emphasis on the blade. One can use a knife without a handle but one cannot use a knife without a blade, therefore the blade is the essence of the knife.
What makes an object superior to another is the quality of their essence. When it comes to the knife, the quality of the blade is what makes one knife superior to the other. Concerning humans, it is widely believed that our mind and wisdom is what separates us from the rest of the animal kingdom. Our mind is our essence and the quality of a man is measured by the quality of his mind.