From Bulbapedia, the community-driven Pokémon encyclopedia.
The Palace of Victory in the anime
The Palace of Victory (Japanese: ウィナーズパレス Winners' Palace) was built to honor Pokémon Trainers who have won the Winner's Trophy. Its less formal title is the Orange League Hall of Fame. It is located on Pummelo Island, next to Pummelo Stadium.
Photos, displays, and trophies are set up to honor every Trainer who has been victorious in the Orange League since the establishment of the Winner's Trophy. Lining the halls of the palace are statues of Dragonite, the guardian of the island.