With all the recent World Cup excitement, I had a thought. How about a challenge to map a playing field? Could be for an athletic game, or maybe an oversized chessboard type thing. I suppose even a simple gladiatorial pit would qualify. Could be a simple variant on an existing game or something wildly original. Coming up with the game to be played on it would be a good exercise for all world-builders. Sports and games often get overlooked, but they're an important part of designing a culture.