Sisyphus cheated death and managed to remain on earth even after the gods had condemned him to die. When they at last got hold of him, they punished his insolence by setting him a dreadful task. Sisyphus had to roll a large boulder up a mountain in the Underworld; and every time he would reach the top, the boulder would slip from his hands and roll back down again. Then, Sisyphus had to walk back and begin his task anew - and so on, through eternity.
Sisyphus is a game of turn-based narration. One player should volunteer to begin the game; after that, proceed in clockwise direction.
During your turn, you must narrate how Sisyphus, starting at the bottom of the mountain, rolls his stone up the mountain, then sees it roll down again and goes back to fetch it. Within these confines, you are free to narrate what you will. You can either narrate the whole cycle, or zoom in on one part of it; you can add events unmentioned by the myth, or tell the tale stark and simple; you can tell a symbolic, an expressionist, a psychological, or any other kind of tale you wish; you can focus on the weight of the stone or the memories of Sisyphus' life on earth, on his moment of despair or his moment of happiness, on his actions or his thoughts - but most of all, you should try to keep your audience interested by telling the tale in a way that has not been heard before.
How do you do that? Not by being the world's best storyteller, but by putting something of yourself into Sisyphus, by opening yourself to the absurdity of the tale and trying to find out what it means to you.
There is no endgame. Of course, at some point the game has to end, but that point has no more meaning and is chosen just as arbitrarily as the point of death where each human life terminates. The labour of Sisyphus goes ever on, even after the last game of Sisyphus has been played and long forgotten.
Albert Camus' The Myth of Sisyphus.