Acuity Cavern

Lake Acuity [ a ] is a location in the Sinnoh region, and part of the Alabaster Icelands in the Hisui region. At the center of the lake, there is a cave that is named Acuity Cavern, which is home to the Legendary Pokémon Uxie, the guardian of the lake and the Being of Knowledge. According to Volo, the lake contains seawater, though nobody knows whether this is due to something in its geography or because of a Pokémon. During the events of Pokémon Diamond, Pearl, Platinum, Brilliant Diamond, and Shining Pearl, Jupiter of Team Galactic captures the Legendary Pokémon living in the lake, easily defeating Barry who had tried to defend it. After Cyrus has been defeated at Spear Pillar / in the Distortion World, Uxie returns to the Acuity Cavern in the middle of the lake.