Elysium

Elysium (also known as Ēlýsion pedíon, Elysium Fields and/or Elysian Fields) is located in the Underworld.

Description
Initially separate from the Underworld, Elysium was reserved for good mortals, heroes, and demigods who had died a hero's death and lived a good life. Chosen by the gods, the souls of mortals, and demigods who have been good, righteous, heroic, would remain after death to live a blessed and happy eternal death, and indulge whatever employment they had enjoyed in life.

Elysium is a gated community with golden gates and laughter can be heard from inside. One can smell barbecue cooking from inside as well. The lands of Elysium also has Greek buildings, Roman marble mansions, and Victorian villas everywhere.

Compared to the Fields of Asphodel and even the Fields of Punishment, Elysium was one of the fewer realms in the Underworld, which also contains the Isles of the Blest. The Isles of the Blest is a large island that resides in Elysium, and borders the lands or fields of Elysium. It is described as having shady parks, with residents indulging their athletic and musical pastimes and surrounds a lake. If heroes choose to be reborn three times and achieve Elysium in all three, they are invited to the Isles of the Blest.

The Lightning Thief
When entering the Underworld for the first time, Percy Jackson sees Elysium in the distance.

The Last Olympian
While talking with Percy, Nico di Angelo tells him that he spoke to Charles Beckendorf's ghost in Elysium. Annabeth tells Luke that he will reach Elysium, but he says that he will try for the Isles of the Blest. Also, Artemis asks Hades to send al the fallen Hunters to it.

The Son of Neptune
Hazel Levesque is given the chance to go to Elysium for successfully stopping Alcyoneus from rising, but her mother will be sentenced to the Fields of Punishment. Hazel begs that her mother will be spared as in the end, she tried to save them both, and the judges allow them to go to the Fields of Asphodel. Whilst in Asphodel, she sees the artificial sunlight reflecting off the water and sees heroes sun bathing, in Elysium and the Isles of the Blest, when she takes Frank Zhang with her in one of her flashbacks.