Which publication prints tough puzzles?

Answer by  Clambake39 (142)

Mensa International puts out a number of books of difficult quizzes and logic puzzles. As a society of people with genius-level intelligence, their puzzles should hopefully meet your criteria.

Answer by  leilich (247)

Your best bet is to identify authors of puzzle collections and look at their publications, mostly in paperback. Puzzlers like Will Shortz of the New York Times, Gary Gruber PH.D. and Charles Barry Townsend search the world and get permission to collect and publish the toughest puzzles.