Basically act as the GM as the PCs explore an island. Maybe there is a mystery to solve or something interesting to explore! I tried to leave the 'ancients' pretty vague on purpose, but any future islands may or may not include things left behind by them.

Ideally, each player would get the chance to create an island. 

(I am using the term island pretty loosely. Maybe someone decides to use their turn as GM to have us attacked by a sea monster!)

The only rule I think I'd put in place would be a time limit... if the game is waiting for the GM for more than 3 (?) days, I may take it over again to prevent the RP from dying.