Old_Geezer is correct. I know lots of people from the quizzing fraternity who, at first glance, appear to be unbelievably intelligent. However, that assumes that your definition of intelligence is the ability to learn inconsequential lists and minutiae that provide no useful function in their daily lives, other than to be good at quizzing.
The easiest way to gain knowledge is to do just that - sit down with a book of facts that you can buy from any branch of W H Smith, and learn it parrot-fashion.
But, if you want to gain real intelligence, then you need to learn from other intelligent people. So start with the great works of literature and immerse yourself in them.