User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4521561-20130918210923/@comment-10901795-20130919160528

That makes sense, they would want to get out of tartarus into a more controled area of the underworld (even punishment) they won't manage it though. It's cool how the tartarus air is poisonus. I think to servive this river, Percy will have to use his slight resistance to fire. It may be that as we have mention to Phlegethon and Cocytus, we must have a mention to Acharus. If they do escape tartarus, percy must be carful as the rocks there are very sticky and when theseus sat down on one, he couldn't get up for 11 months untill Hercules came and lifted him up. His but got torn of and it is still there to this day.

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