From Bulbapedia, the community-driven Pokémon encyclopedia.
The Eterna Historical Museum (Japanese: ハクタイ歴史博物館 Hakutai Historical Museum) is an anime-exclusive building located in Eterna City in Sinnoh. It appeared in A Secret Sphere of Influence, in which it was visited by Ash, Dawn, Brock, and Nando.
Among the many artifacts inside the museum are a scale model of the Space-Time Tower; statues of Uxie, Mesprit, and Azelf; and the Adamant Orb, the latter of which Team Rocket tried to steal while under the direction of Team Galactic. The Adamant Orb is no longer under its possession, as it was stolen by Team Galactic while it was being taken to Celestic Town for research in Losing Its Lustrous! via a police plane.
Also inside the museum are the many Sinnoh myths and legends. Outside, there are statues of the Legendary Dialga and Palkia.