Quote from : The House of Hades Book

So . . . what is this fire river called?” “The Phlegethon,” [Annabeth] said. “You should concentrate on going down.” “The ?” [Percy] shinnied along the ledge. They’d made it roughly a third of the way down the cliff—still high enough up to die if they fell. “Sounds like a marathon for hawking spitballs.” “Please don’t make me laugh,” she said. “Just trying to keep things light.