What about a culture of nomadic sea folk who live on the backs of giant sea tortoises? They control the tortoises by feeding them some sort of plant that makes the tortoises amenable to their commands (ie enslaved). These folk drift apart much of the year as they fish and harvest plants from the sea, but once every year they band together before monsoon season to exchange kin, share stories and otherwise prepare for the storms.
They would be expert fishermen, know the surrounding seas like the backs of their hands, and probably have very unusual marriage/family customs. They'd be metal-poor, but rich in crafts and oral lore. They might be evil, enslavers of sea creatures, or they might simply be neutral, not putting any thought into the moral wrongness of their culture's actions.