The Pokémon League is built at the summit of Mount Lanakila over where the final island challenge of defeating all four island kahunas in a row used to be held. According to Professor Kukui, who founded the League, it is built on the highest place in Alola and closest to the sunSUS/moonMUM in order to honor and respect SolgaleoSUS/LunalaMUM.
The central chamber of the League building is a large room shaped in a half-circle with paths leading to a chamber for each Elite Four member. When a member of the Elite Four is defeated, a light will flow from that chamber to the platform in the middle of the central chamber. Once all four outer chambers feed light into the central chamber, the platform will teleport the player to the Champion's chamber.
Following the tradition since Generation V, the Elite Four can be challenged in any order.
In Pokémon Sun and Moon, Hala's chamber can be accessed through the leftmost path of the central chamber. In Hala's chamber, he greets the player in his new role as one of the Trainers chosen to reign as the Elite Four in Alola. Two fists made of light emerge from the pedestal behind Hala after the player enters to close off the arena, preventing the player from leaving.
In Pokémon Ultra Sun and Ultra Moon, Molayne, Professor Kukui's old friend, takes Hala's place as a member of the Elite Four. After greeting the player, gray hexagons emerge and surround the player, locking them in the chamber until they defeat him.
Olivia's chamber is called the Rock Chamber and can be accessed through the middle-left path of the central chamber. In the Rock Chamber, Olivia will dismiss pleasantries in favor of simply battling. Two cliff-like structures made of light emerge from the pedestal behind Olivia after the player enters to close off the arena.
Acerola's chamber can be accessed through the middle-right path of the central chamber. In Acerola's chamber, she greets the player and tells them that she's there in place of Nanu, who refused the invitation to be part of the Elite Four. Two purple ghastly flames emerge from the pedestal behind Acerola after the player enters to close off the arena.
Kahili's chamber can be accessed through the rightmost path of the central chamber. In Kahili's chamber, she greets the player and introduces herself, noting her own history with the island challenge and how she was invited to join the Elite Four. Two green wings made of light emerge from the pedestal behind Kahili after the player enters to close off the arena.
The Champion's chamber is located at the topmost part of the league, surrounded by transparent crystal-like windows, which shows the scenery of the sky and land of Alola clearly. The chamber differs from the others slightly. It has two circular platforms, with the first leading up to the other via a flight of stairs. The second platform is empty except for a throne-like seat.
In Pokémon Sun and Moon, once the player sits on this throne, Kukui will appear and challenge the player to ensure their worthiness as Alola's first Champion, as well as to celebrate the beginning of Alola's new Pokémon League. In Pokémon Ultra Sun and Ultra Moon, Hau will appear and challenge the player for the title instead.
Once the player attains the title of Champion, the incumbent will simply approach the throne and take their seat, awaiting the arrival of the next challenger.