A picture of Mount Tamalpais in California. In multiple books in the series, this is the location of the Garden of the Hesperides and Mount Othrys.
https://www.parks.ca.gov/ImageGallery/?page_id=471
A picture of the North Shore of Long Island, New York. Throughout the series, this is the location of Camp Half-Blood.
A picture of the South Shore of Long Island, New York. This is the opening location of The Last Olympian where Percy is hanging out with Rachel Elizabeth Dare.
A picture of the Plaza Hotel in New York City. In The Last Olympian, this is where Percy and his friends go to recuperate during the battle.
A picture of Central Park in New York City. This is another entrance to the Underworld in The Last Olympian that Percy and Nico use to get to the River Styx.
https://unsplash.com/photos/A2CChTZvzTE
A picture of Battery Park in New York City. In The Last Olympian, Battery Park is the location where Percy goes to talk with the East and Hudson Rivers.
https://unsplash.com/photos/b4kGBj8cIEg