The Economist writes on what is considered the most intellectually challenging game of them all:
[Go] is a simple parlour game where two opponents, comfortably seated and often equipped with nothing more than folding paper fans and cigarettes, take turns placing little stones, some black, some white, on a flat wooden grid. Simple regarding rules and gear, that is, yet so challenging that in this mind-game, unlike chess, and despite the long-standing offer of a $1.6m reward for a winning program, no computer has yet been able to outwit a clever ten-year-old.
The game…is not just more difficult and subtle than chess. It may also be the world’s oldest surviving game of pure mental skill. Devised in China at least 2,500 years ago, it had stirred enough interest by the time of the Han dynasty (206BC-220AD) to inspire poets, philosophers and strategic theorists. One of these strategists, Huan Tan (who died in 56AD), advises in his work Xin Lun, or New Treatise, that the best approach in the game is to spread your pieces widely so as to encircle the opponent. Second best is to attack and choke off enemy formations. The worst strategy is to cling to a defence of your own territorya warning that would have benefited, say, the designers of France’s 1930s Maginot line.