Grey Labyrinth - A playground for the curious mind where the thoughts, riddles and paradoxes presented are meant as a lure to explore the limits of perception and knowledge. Once you've solved this one the puzzle archive provides access to past puzzles. One for a clear head. This page gives you the opportunity to try a number of different strategies and see which works best. Games, lessons, activities, demonstrations and software, all related to fractals and chaos, can be found on this site which caters for all levels of abilities and knowledge.
Access is via an optional registration form.
Grand Illusions - This site is, in their own words, 'for the enquiring mind, with optical illusions, scientific toys, visual effects and even a little magic'. Discover oriental magic mirrors that reflect the image of Buddha from thin air and read how Napolean was poisoned by his wallpaper. If after getting your eyes twisted around an optical illusion you need an additional challenge, try your luck at solving a challenging scientific puzzle. There's also a page where you can vote for your favorite Math quotations, but so far there are only seven there. Beatcalc - This site gives instructions on how to receive a weekly math puzzle which will exercise your brain.