Currently re-reading Percy Jackson and goodness the books have aged incredibly well IMO. Still gotta finish Trials of Apollo, but it’s been so long that I need a refresher.
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I don't remember the Valhalla place well. But as far as standards for living and life goes... New Rome. Percy even mentioned it has better long term living conditions than Camp Halfblood. Camp halfblood is a cool summer camp place, but not really great for permanent living.