You’ll know you’re almost to the Rosetta Stone when you find a floor populated by mermaids. There are no enemy encounters here, so take your time and collect all of the treasure chests. This floor is unique in that it wraps when you reach an edge. The room containing the Rosetta Stone is in the North East, but you must pass through the opening in the North West to reach it.
After getting the Rosetta Stone, return to the entrance of the shrine and take the westernmost staircase. This path is slightly longer than the one you were just on, so if you are running low on health, magic, or items, now would be an ideal time to return to the surface.
After climbing several floors and collecting a modest amount of treasure, it will be time to battle the Kraken, the Fiend of Water!