The Fourth Strata

From publisher blurb: Beneath the swamps of the Third Strata, lies the Fourth Strata. It's many rivers are fed by the falling water from the Third Strata's swamps. The rivers are not the kind, gentle streams found higher up in the Great Chasm, oh no. They are raging torrents of water that slice through the land, cutting through ground and rock! It is also where the richest artifact finds are made! As the rivers cut through the soil, they uncover ruins and caches of ancient items. And many artifacts. And the richest source is the Lost City of Vidra. The waters uncover it in one location and then bury it, only for it to appear somewhere else. This is the domain of the Black Cloak Masters, it is full of wonder and danger. Are you strong enough to explore it's rocky islands amongst the rapids?