Seattle is a coastal seaport city in Northwestern Washington. It is the largest city in the Pacific Northwest, with over 600,000 residents.
Hermes confronts Percy Jackson after the Titan War to ask him if he will make sure his other demigod children arrive safely at Camp Half-Blood. He says that there are a pair of twins in Seattle, a boy and a girl.
Percy Jackson, Hazel Levesque, and Frank Zhang visit the city during their quest to free Thanatos in Alaska. There they went to the company Amazon's Headquarters in Seattle to discover the infamous Amazons to be running the company. Their leader, Hylla Ramírez-Arellano, turns out to be the sister of Reyna Ramírez-Arellano, praetor of Camp Jupiter. This is also the place where they meet Arion.