Considered by many to be the hardest riddle on the internet, Notpron is an online puzzle made in 2004 by David Münnich. There are 140 levels in total, and your goal is to start at level 1 and continuously progress through the levels. It starts out simple enough but quickly becomes challenging, requiring players to use a variety of tactics just to acquire more hints. There have been 15.5 million visitors to the site, but only 27 have successfully solved all 140 levels.
If you have some time to kill and feel like pushing your problem solving skills to the limit, try it out and see how far you can make it. If you have played before, share in the comments how far you made it and what you thought about it.
Think you have what it takes? Head to www.deathball.net/notpron to find out.