The game of chess is played in many parts of the world, but it isn't truly an immutable constant. It's descended from a different game, and other games also descended from that one. The relative of chess that I find most intriguing is Japan's shogi, whose name means "general's game."
Unfortunately, shogi is a counter-intuitive game for a chess player; pieces generally have rather bizarre movesets rather than chess's hyperstandardized ones (chess's memorable simplified moves were arrived at after centuries of simplification), and it's difficult for someone who can't read Japanese characters to keep the pieces apart, as the pieces pretty much all look the same. Further, capturing and promoting work rather differently-when you capture a piece, while it is removed from the board, it becomes yours to "drop" or deploy back onto the board.
The real reason the game fascinates me is because of the numerous alternate rulesets that are known to exist. True to Japan's nature, they invented more different ways to play the game that were hideously and hilariously bizarre and complicated. The most notable variations on this idea are the "dai shogi" ("great" or "big" shogi) variants.
Of these, Wikipedia notes: "It is thought that the really huge games (dai shogi and up) were never really played to any significant extent and were devised merely so that the creators could have the fun of inventing enormous games, amazing their friends and confounding their enemies."
Let's look at a few of the rules on size for these games...
Dai dai shogi ("big, big" shogi): 17x17 board, 289 squares, 96 pieces per player, 64 piece types, and 68 move types. (The reason there are more movement types than piece types is because you promote a piece by flipping it over, and the promoted piece has its own often entirely new move type or moveset. Fortunately, many pieces promote into pieces virtually identical to other pieces, and many different pieces will promote into the same pieces.)
Tai shogi ("grand" shogi): 25x25 board, 625 squares, 177 pieces per player, 93 piece types, and 96 move types. (I have an old program that only runs on pre-2000 versions of Windows that will run shogi variants up to tai shogi. In fact, I was able to find a YouTube video of someone playing tai shogi with the same or a similar program. It looks... byzantine-if you pay attention towards the middle, each side seems to set up huge lines and advance in waves, in a way that, if you're familiar with chess, looks impossible.)
Taikyoku shogi ("ultimate" shogi): 36x36 board, 1,296 squares, 402 pieces per player, 209 piece types, and 253 move types.
Here's a diagram of taikyoku shogi's piece setup (lifted from Wikipedia). (You can also find pictures of the setup here.)
After a brief calculation, a board for taikyoku shogi with 1.5" squares (there's no information on how big a shogi board's squares traditionally are, so I checked a chess board I dug up) would be four and a half feet to a side.
Yeah, I don't think that would be too practical. (For that matter, tai shogi is slightly too big for my old computer's monitor, and I have to tweak the heck out of it to see the whole board.) I suppose it's just as well nobody's really sure how to actually play taikyoku shogi. (That is to say, nobody knows absolutely for sure what all the rules are.)