A reader mentioned the great Jacques Barzun. Years ago I had a friend who took a semester from Stanford only to take Barzun's famous cultural history and philosophy course at Columbia. It wasn't a course you could "take." You had to be approved for it and had to commit to it. Sometimes he would interview students to make sure they were up to it.
It was 3 books to read/week, and you had to stand and deliver in class. High standards for an undergrad (and grad) class. Barzun also never gave an A. He told the kids that nobody could digest all of this to his expectations. It was an academic humanities boot camp.
My pal, who had far more IQs than me, went on to a brilliant academic career and has always praised Prof. Barzun for it.
For an intro to Barzun, you can try A Jacques Barzun Reader: Selections from His Works