Ooh, I didn't know about National Puzzle Day. In the last couple of years, I've fallen down the rabbit hole of variant sudoku, which is something I did not realize existed until I watched this video (that got linked in a fannish community) and got hooked first on the puzzle-solving channel and then on solving them myself. My favorite of these puzzles recently have been these rat maze puzzles which combine, well, mazes with a number of variant sudoku constraints, along with a cute rodent drawing, which automatically makes them the best :)