The human myth is that a Greek philosopher named Plato had been told the story of the island of Atlantis by his father, Solon, who had been told the story by an Egyptian priest who was carving it into a column for a temple. The island was in the era 9600 BC. However, after its people tried to invade Athens, in a single night and day of misfortune the island of Atlantis sank into the depths of the ocean. Dozens of possible locations for the city have been suggested, including Santorini, Greece, Azores in the Atlantic, and off the coast of Cornwall in New England.
Atlantis is as big as the city on Mount Olympus, with wide courtyards and columned pavilions. Twenty or thirty buildings are made of abalone, white but gleaming with rainbow colors. Fish and octopi dart in and out of the windows. The gardens are full of exotic sea plants and coral colonies, with luminescent jellyfish drifting about like Christmas lights.
In Percy Jackson's Greek Gods, the Palace of Atlantis was described to be a big mansion made of pearl, sea stone, and abalone shell. The paths are lined with glowing pearls, the doorways are huge, and the roof has a big open deck that had been set up as a command center. Poseidon's throne is made of coral. A mosaic on the floor shows an exact map of the palace grounds and the surrounding ocean. Colored stone tiles represent different armies and sea monsters shift around as the forces change position.
Percy at the end of the book has a dream of him following Tyson into the court of Poseidon. He sees his father in a magnificent hall with cobbled floor of pearls and Poseidon sitting on a throne of coral. He tells Percy to 'Brace yourself' just like he said in the letter delivered by Hermes. Tyson got an internship working in the Underwater Forges of the Cyclopes to make weapons for the Olympians for the upcoming war.
Percy sent Tyson an Iris Message in Atlantis, where Tyson talked about his new job and how some of the older sea spirits were making trouble for Poseidon in Atlantis, waging war against him.
Tyson found Percy Jackson drifting underwater after Percy escapes from Kronos' grasps and Luke Castellan's cruise ship, Princess Andromeda, exploded and took him to the palace. He said the palace was the size of Mount Olympus. There he saw several of mermen in the courtyard. The palace was in the process of being destroyed by the Titan Oceanus whom Poseidon was fighting his own war against. In the throne room he met his father Poseidon, his stepmother Amphitrite, his half-brother Triton, and Delphin, the god of dolphins. Poseidon's appearance is an old man, as he reflects the state of his palace, and he is watching a mosaic that mirrors his kingdom, with every building being destroyed in reality is shown on the mosaic. Poseidon then sees Oceanus approaching and bids goodbye to Percy so he could fight Oceanus in his true godly form.
- Curiously, in The Blood of Olympus, Percy specifically says to Jason Grace that Atlantis doesn't exist, implying that it is separate from Poseidon's realm.