User blog comment:SayuriDarling/The Blood of Olympus Official Discussion/@comment-3146930-20141013211630/@comment-1820614-20141014023855

I think the Giants went to Athens instead of Olympus because when people think of Olympus it is more in a sense of an Olympian city on a mountain like what floats over New York. Ask most people about the actual Mt. Olympus and they think of it only as a mountain somewhere in Greece. Athens the city is what most people think of when they think of Greek Culture:  architecture, philosophy, art, religion, etc. It would be considered the origin of Western Civilization. Not the top of some remote mountain. And Western Civilization is what the Olympians are tied to and the true source of their strength. Athens is where the Western Civilization the Olympians are tied to truly got its start and is the most well known location among humans. Not a specific mountain.

I don't recall Hercules guarding the gates of Olympus. IIRC, he originally thought his job as gatekeeper applied to the metaphysical Olympus. Instead, he is guard to the ancient lands. I don't recall if it was ever stated why the ancient lands were forbidden. Maybe there were certain relics and secrets the Olympians wanted to keep hidden? Maybe Zeus only wanted a convenient reason to keep Hercules far away from Olympus to prevent fighting with Hera. We know this version of Zeus is a bigger jerk than most.

I look at Calypso's comments as one who has been under house arrest for a very, very long time. She made the island a home because she was trying to make the best of a bad situation. Ultimately, it was a prison. She could either suffer and treat it as such or try and make it not so bad. If she were to ever return she would be reminded of her long imprisonment and centuries of loneliness.