User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-6064271-20130608181112/@comment-3146930-20130608233253

Another reason to re-read the series is because they make a lot of references to the PJO series in the HoO series. I mean I remember in The Mark of Athena when Percy mentioned the dam hole. No one got it and Percy passes it off as an inside joke. For me, it became funnier when I noticed that no one at the Hoover Dam was at Camp Jupiter at the time or even in the book.