Black Belt Crosswords by Rich Norris
This book comes from puzzle sensei Rich Norris, one of the most prolific authors of the New York Times crosswords in the last 20 years. It includes 300 super-tough puzzles. You can expect to flex your mental muscles to the utmost! If you can complete these mind-meltingly tough conundrums, you're a true crossword expert and a solver of the highest skill.