The Quiz Zone: There's a huge number of websites out there where you can stretch the grey matter. Whether it's IQ, Pub Quizzes, Crosswords, Sudoku or general knowledge, here's some recommended links
Notpron has been online since 2004 and is regarded as the hardest challenge there is on the Internet. 0.0001 percent of players ever finish. You need a good understanding of computers for starters. An analytical mind and the ability to search for and download programs to help you through the challenge. Bet you won't get past level 3 and there are 140!