Aqua Hideout is a location in Hoenn. It is located near Lilycove City. It is the base of operations for the criminal organization Team Aqua in Pokémon Sapphire and Pokémon Emerald. It was raided by the player. After the group's disbandment, this location is left empty and desolate.
Before entering the hideout, the player will notcie that Team Aqua is stealing the submarine from Slateport City. The player then must traverse the hideout before continuing on since an Aqua Grunt training his Wailmer is blocking the sea path.
If the player talks to the man near the steps leading to the beach in Lilycove City, they will learn that the cave in which the Hideout is located was once a beautiful, natural feature, until Team Aqua takes over.