Everybody loves a good puzzle. There’s a certain satisfaction in figuring out the answer to a difficult riddle. Plus, research shows riddles and puzzles keep your brain sharp in old age.
The internet is a repository of mind-bending puzzles . But many of these require you to have technical skills, like looking up the source code of a page for clues or altering image files. Logic should test your brain, not your computer skills.
We can’t say if these are the “hardest” puzzles online. What we can say for sure is that these five brain-teasing sites are loved by anyone who likes solving stuff.
NSA’s Puzzle Periodical (Web): One Difficult New Puzzle, Every Month
The National Security Agency has a bad rep among internet users because of its spying and infringements of privacy . Set that aside for a minute and you’ll know that some of the brightest minds work there. And every month, one of these bright minds submits a puzzle for the world to figure out.
The NSA Puzzle Periodical was started only last year, so there isn’t a large collection waiting for you. But you can still browse through logic puzzles, written precisely and exquisitely. Most importantly, it’s a new puzzle every month!
The answer is posted a few days after the question, so feel free to discuss it with others till then. There are no trick questions or cheap answers, as far as I can make out.
Sudoku Escargot (Web): The Hardest Sudoku Ever
You’re probably familiar with the numbers-oriented game of Sudoku. It’s a stress-free way to give your brain a 5-minute workout . You might already be pretty good at it. But do you think you can solve the hardest Sudoku puzzle ever made?
Mathematician Arto Inkala built an algorithm to generate challenging Sudokus, called AI Sudoku. And this is the most difficult one the bot ever created. It’s called the Escargot, and on his blog, Inkala explains why it’s the most difficult Sudoku.
Try solving it on Sudoku Wiki or print it out and take it with you. No matter how you choose to tackle this, make sure you have plenty of time. And Inkala’s blog post linked above also has 19 other super-difficult Sudokus for you to solve.
Blue Eyes (Web): XKCD’s “Hardest Logic Puzzle”
I love getting a difficult puzzle that I can slowly work on, over several days or weeks. The joy of a good riddle lies as much in the journey. If you’re patient with puzzles, then read “the hardest logic puzzle in the world,” according to XKCD.
For the uninitiated, XKCD is one of the best webcomics for geeks , often talking about logic, math, and lateral thinking. Its creator shared this puzzle (which he heard from someone else) in the simplest language possible. No word play, no double meanings, or anything else.
Read the riddle, digest every information from it, and set about working it out in your head. You’ll find yourself thinking about it whenever you have some time.
101 Friday Puzzles (Web): Richard Wiseman’s 101 Brainteasers
Noted psychologist Richard Wiseman is a bit of an internet celebrity. He is known for amazing illusions that blow your mind on his YouTube channel, he is a noted expert on magic and psychology, and he is a famed logician.
Every Friday, Wiseman shares a puzzle or riddle on his blog, challenging readers to solve it. The puzzles use a combination of linear and lateral thinking, so some answers will require creative thinking.
You’ll find matchstick problems, logical riddles, and some picture-based puzzles too. There are 101 to get through, so save this page for offline reading wherever.
Logic Mazes (Web): Robert Abbott’s Famous Puzzles
Logician, programmer, and game inventor Robert Abbott has been designing games since the 1950s. Abbott pioneered the concept of “logic mazes”, and some of his best ones are available online for free.
A logic maze is a maze or a grid with some set rules. For example, the Easy Maze 1 dictates you can never turn left. So without turning left, how do you travel from the start to the finish line?
Abbott also makes interactive puzzles that are hosted on the site, so you can “play” instead them to solve. Trust me, you’re going to need that little interactivity if you want any hope of getting through these.
Can You Solve This?
You can solve any of the logic questions above, or you can try your hand at figuring out this fun puzzle.
You have 16 marbles and a balancing scale. One of the marbles is heavier or lighter than the others, while 15 are the same weight. Using the scales three times or less, identify the odd marble and whether it’s heavier or lighter.
If these puzzles are too much for you, have a look at these relaxing puzzle games for iPhone .