Possible Clues:

• River in Hades
• Mythical river
• River of Hades
• River of woe, in Greek myth
• A river of Hades
• The pain the boy gets from this infernal flower
• Somehow reach no infernal river
• Long river where there's no returning?
• That's one hell of a river so to cause pain to Ronald
• Greek myth’s “river of woe”, crossed by souls of the dead